case study questions class 9 science chapter 4

Class 9 Science Case Study Questions Chapter 4 Structure of Atom

• Post author: studyrate
• Post published:
• Post category: class 9th
• Post comments: 0 Comments

Case study Questions on Class 9 Science Chapter 4  are very important to solve for your exam. Class 9 Science Chapter 4 Class 9 Science Case Study Questions have been prepared for the latest exam pattern. You can check your knowledge by solving  case study-based questions for Class 9 Science  Chapter 4 Structure of Atom

Join our Telegram Channel, there you will get various e-books for CBSE 2024 Boards exams for Class 9th, 10th, 11th, and 12th.

In CBSE Class 9 Science Paper, Students will have to answer some questions based on Assertion and Reason. There will be a few questions based on case studies and passage-based as well. In that, a paragraph will be given, and then the MCQ questions based on it will be asked.

Structure of Atom Case Study Questions With Answers

Here, we have provided case-based/passage-based questions for Class 9 Science  Chapter 4 Structure of Atom

Case Study/Passage-Based Questions

Case Study 1: The maximum number of electrons that are permitted to be assigned to an energy shell of an atom is called the electron capacity of that shell. The distribution of electrons in different orbits or shells is governed by a scheme known as the Bohr-Bury scheme. According to this scheme : (i) The maximum number of electrons that can be present in any shell is given by the formula 2n2 where n is the number of energy levels. (ii) The maximum number of electrons that can be accommodated in the outermost shell is 8. Electrons are filled in the shells in a stepwise manner in increasing the order of energy of the energy shell.

What is the maximum electron capacity of the N shell? (a) 24 (b) 8 (c) 18 (d) 32

Answer: (d) 32

Identify the element with the configuration K-2, L-8, M-3. (a) Aluminium (b) Magnesium (c) Sodium (d) Beryllium

Answer: (a) Aluminium

Which of the following configuration represent sodium? (a) 2, 8, 4 (b) 2, 8, 5 (c) 2, 3 (d) 2, 8, 1

Answer: (d) 2, 8, 1

Case Study/Passage Based Questions

The given diagrams show the atomic structures of elements X and Y.

Element X and Y could be _ and _ respectively. (a) Be and B (b) C and O (c) F and N (d) C and N

Answer: (d) C and N

Valency of elements X and Y are respectively, (a) 4 and 3 (b) 2 and 5 (c) 1 and 4 (d) 3 and 4

Answer: (a) 4 and 3

Elements X and Y are (a) isotopes (b) isoelectronic (c) isobars (d) isomers.

Answer: (c) isobars

Case Study 2: The mass of an atom is due to the masses of protons and neutrons in the nucleus. The relative masses of protons and neutrons are almost equal to one. Therefore, the atomic mass of an element should be nearly a whole number. But in many cases the atomic masses are fractional. The main reason for these fractional atomic masses is that these elements occur in nature as a mixture of several isotopes. The atomic mass of an element is the average of the atomic masses of these isotopes in the ratio of their proportion of occurrence.

Chlorine occurs in nature in the form of two isotopes with atomic masses 35 u and 37 u in the ratio of 3 : 1 respectively. The atomic mass of chlorine is (a) 35.5 u (b) 34.5 u (c) 35 u (d) 36 u

Answer: (a) 35.5 u

An element occurs in two isotopic forms with atomic masses 10 and 11. What is the percentage abundance of two isotopes in the sample having an atomic mass of 10.80? (a) 20, 80 (b) 50, 50 (c) 25, 70 (d) 60, 40

Answer: (a) 20, 80

The fractional atomic masses of elements are due to the existence of (a) isotopes having different masses (b) diagonal relationship (c) equal number of electrons and protons (d) none of these.

Answer: (a) isotopes having different masses

Case Study 3: The structure of an atom consists of subatomic particles, mainly protons, neutrons, and electrons. Protons and neutrons are located in the nucleus, which is the central region of an atom. Protons carry a positive charge, while neutrons are electrically neutral. Electrons, on the other hand, are negatively charged particles that orbit around the nucleus in energy levels or shells. The number of protons in an atom determines its atomic number, which is unique to each element. The mass number of an atom is the sum of its protons and neutrons. The atomic mass of an element is the weighted average mass of all its naturally occurring isotopes. Isotopes are atoms of the same element that have different numbers of neutrons. The arrangement and distribution of these subatomic particles determine the overall stability and properties of an atom.

Which subatomic particles are mainly located in the nucleus of an atom? a) Protons and electrons b) Neutrons and electrons c) Protons and neutrons d) Protons, neutrons, and electrons Answer: c) Protons and neutrons

What is the charge of protons? a) Positive b) Negative c) Neutral d) Variable Answer: a) Positive

Where are electrons located in an atom? a) Nucleus b) Energy levels or shells c) Protons d) Neutrons Answer: b) Energy levels or shells

What determines the atomic number of an atom? a) Number of electrons b) Number of protons c) Number of neutrons d) Sum of protons and neutrons Answer: b) Number of protons

What are atoms of the same element with different numbers of neutrons called? a) Isotopes b) Ions c) Elements d) Electrons Answer: a) Isotopes

Hope the information shed above regarding Case Study and Passage Based Questions for Class 9 Science Chapter 4 Structure of Atom with Answers Pdf free download has been useful to an extent. If you have any other queries about CBSE Class 9 Science Structure of Atom Case Study and Passage Based Questions with Answers, feel free to comment below so that we can revert back to us at the earliest possible By Team Study Rate

You Might Also Like

Class 9 maths case study questions chapter 14 statistics, mcq questions of class 9 maths chapter 15 probability with answers, class 9 maths case study questions of chapter 10 circles pdf download, leave a reply cancel reply.

Save my name, email, and website in this browser for the next time I comment.

CBSE Expert

Case Study Questions of Chapter 4 Structure of Atom PDF Download

Case study Questions on Class 9 Science Chapter 4  are very important to solve for your exam. Class 9 Science Chapter 4 Case Study Questions have been prepared for the latest exam pattern. You can check your knowledge by solving case study-based questions for Class 9 Science Chapter 4 Structure of Atom

In CBSE Class 9 Science Paper, Students will have to answer some questions based on Assertion and Reason. There will be a few questions based on case studies and passage-based as well. In that, a paragraph will be given, and then the MCQ questions based on it will be asked.

Structure of Atom Case Study Questions With answers

Here, we have provided case-based/passage-based questions for Class 9 Science  Chapter 4 Structure of Atom

Case Study/Passage Based Questions

The maximum number of electrons that are permitted to be assigned to an energy shellb of an atom is called the electron capacity of that shell. The distribution of electrons in different orbits or shell is governed by a scheme known as Bohr-Bury scheme. According to this scheme : (i) The maximum number of electrons that can be present in any shell is given by the formula 2n2 where n is the number of energy levels. (ii) The maximum number of electrons that can be accommodated in the outermost shell is 8. Electrons are filled in the shells in a stepwise manner in increasing the order of energy of the energy shell.

What is the maximum electrons capacity of the N shell? (a) 24 (b) 8 (c) 18 (d) 32

Answer: (d) 32

Identify the element with the configuration K-2, L-8, M-3. (a) Aluminium (b) Magnesium (c) Sodium (d) Beryllium

Answer: (a) Aluminium

Which of the following configuration represent sodium? (a) 2, 8, 4 (b) 2, 8, 5 (c) 2, 3 (d) 2, 8, 1

Answer: (d) 2, 8, 1

The given diagrams show the atomic structures of elements X and Y.

Element X and Y could be _ and _ respectively. (a) Be and B (b) C and O (c) F and N (d) C and N

Answer: (d) C and N

Valency of elements X and Y are respectively, (a) 4 and 3 (b) 2 and 5 (c) 1 and 4 (d) 3 and 4

Answer: (a) 4 and 3

Elements X and Y are (a) isotopes (b) isoelectronic (c) isobars (d) isomers.

Answer: (c) isobars

The mass of an atom is due to the masses of protons and neutrons in the nucleus. The relative masses of protons and neutrons are almost equal to one. Therefore, the atomic mass of an element should be nearly a whole number. But in many cases the atomic masses are fractional. The main reason for these fractional atomic masses is that these elements occur in nature as a mixture of several isotopes. The atomic mass of an element is the average of the atomic masses of these isotopes in the ratio of their proportion of occurrence.

Chlorine occurs in nature in the form of two isotopes with atomic masses 35 u and 37 u in the ratio of 3 : 1 respectively. The atomic mass of chlorine is (a) 35.5 u (b) 34.5 u (c) 35 u (d) 36 u

Answer: (a) 35.5 u

An element occurs in two isotopic forms with atomic masses 10 and 11. What is the percentage abundance of two isotopes in the sample having an atomic mass of 10.80? (a) 20, 80 (b) 50, 50 (c) 25, 70 (d) 60, 40

Answer: (a) 20, 80

The fractional atomic masses of elements are due to the existence of (a) isotopes having different masses (b) diagonal relationship (c) equal number of electrons and protons (d) none of these.

Answer: (a) isotopes having different masses

Hope the information shed above regarding Case Study and Passage Based Questions for Class 9 Science Chapter 4 Structure of Atom with Answers Pdf free download has been useful to an extent. If you have any other queries of CBSE Class 9 Science Structure of Atom Case Study and Passage Based Questions with Answers, feel free to comment below so that we can revert back to us at the earliest possible

Leave a Comment Cancel reply

Save my name, email, and website in this browser for the next time I comment.

Download India's best Exam Preparation App Now.

Key Features

• Revision Notes
• Important Questions
• Previous Years Questions
• Case-Based Questions
• Assertion and Reason Questions

No thanks, I’m not interested!

myCBSEguide

• Class 9 Science Case...

Class 9 Science Case Study Questions

Table of Contents

myCBSEguide App

Download the app to get CBSE Sample Papers 2023-24, NCERT Solutions (Revised), Most Important Questions, Previous Year Question Bank, Mock Tests, and Detailed Notes.

If you are wondering how to solve class 9 science case study questions, then myCBSEguide is the best platform to choose. With the help of our well-trained and experienced faculty, we provide solved examples and detailed explanations for the recently added Class 9 Science case study questions.

You can find a wide range of solved case studies on myCBSEguide, covering various topics and concepts. Class 9 Science case studies are designed to help you understand the application of various concepts in real-life situations.

The rationale behind Science

Science is crucial for Class 9 students’ cognitive, emotional, and psychomotor development. It encourages curiosity, inventiveness, objectivity, and aesthetic sense.

In the upper primary stage, students should be given a variety of opportunities to engage with scientific processes such as observing, recording observations, drawing, tabulating, plotting graphs, and so on, whereas in the secondary stage, abstraction and quantitative reasoning should take a more prominent role in science teaching and learning. As a result, the concept of atoms and molecules as matter’s building units, as well as Newton’s law of gravitation, emerges.

Science is important because it allows Class 9 Science students to understand the world around us. It helps to find out how things work and to find solutions to problems at the Class 9 Science level. Science is also a source of enjoyment for many people. It can be a hobby, a career, or a source of intellectual stimulation.

Case study questions in Class 9 Science

The inclusion of case study questions in Class 9 science CBSE is a great way to engage students in critical thinking and problem-solving. By working through real-world scenarios, Class 9 Science students will be better prepared to tackle challenges they may face in their future studies and careers. Class 9 Science Case study questions also promote higher-order thinking skills, such as analysis and synthesis. In addition, case study questions can help to foster creativity and innovation in students. As per the recent pattern of the Class 9 Science examination, a few questions based on case studies/passages will be included in the CBSE Class 9 Science Paper. There will be a paragraph presented, followed by questions based on it.

Examples of Class 9 science class case study questions

Class 9 science case study questions have been prepared by myCBSEguide’s qualified teachers. Class 9 case study questions are meant to evaluate students’ knowledge and comprehension of the material. They are not intended to be difficult, but they will require you to think critically about the material. We hope you find Class 9 science case study questions beneficial and that they assist you in your exam preparation.

The following are a few examples of Class 9 science case study questions.

Class 9 science case study question 1

• due to its high compressibility
• large volumes of a gas can be compressed into a small cylinder
• transported easily
• all of these
• shape, volume
• volume, shape
• shape, size
• size, shape
• the presence of dissolved carbon dioxide in water
• the presence of dissolved oxygen in the water
• the presence of dissolved Nitrogen in the water
• liquid particles move freely
• liquid have greater space between each other
• both (a) and (b)
• none of these
• Only gases behave like fluids
• Gases and solids behave like fluids
• Gases and liquids behave like fluids
• Only liquids are fluids

Answer Key:

• (d) all of these
• (a) shape, volume
• (b) the presence of dissolved oxygen in the water
• (c) both (a) and (b)
• (c) Gases and liquids behave like fluids

Class 9 science case study question 2

• 12/32 times
• 18 g of O 2
• 18 g of CO 2
• 18 g of CH 4
• 1 g of CO 2
• 1 g of CH 4 CH 4
• 2 moles of H2O
• 20 moles of water
• 6.022  ×  1023 molecules of water
• 1.2044  ×  1025 molecules of water
• (I) and (IV)
• (II) and (III)
• (II) and (IV)
• Sulphate molecule
• Ozone molecule
• Phosphorus molecule
• Methane molecule
• (c) 8/3 times
• (d) 18g of CH ​​​​​4
• (c) 1g of H ​​​​​​2
• (d) (II) and (IV)
• (c) phosphorus molecule

Class 9 science case study question 3

• collenchyma
• chlorenchyma
• It performs photosynthesis
• It helps the aquatic plant to float
• It provides mechanical support
• Sclerenchyma
• Collenchyma
• Epithelial tissue
• Parenchyma tissues have intercellular spaces.
• Collenchymatous tissues are irregularly thickened at corners.
• Apical and intercalary meristems are permanent tissues.
• Meristematic tissues, in its early stage, lack vacuoles, muscles
• (I) and (II)
• (III) and (I)
• Transpiration
• Provides mechanical support
• Provides strength to the plant parts
• None of these
• (a) Collenchyma
• (b) help aquatic plant to float
• (b) Sclerenchyma
• (d) Only (III)
• (c) provide strength to plant parts

Cracking Class 9 Science Case Study Questions

There is no one definitive answer to Class 9 Science case study questions. Every case study is unique and will necessitate a unique strategy. There are, nevertheless, certain general guidelines to follow while answering case study questions.

• To begin, double-check that you understand the Class 9 science case study questions. Make sure you understand what is being asked by reading it carefully. If you’re unclear, seek clarification from your teacher or tutor.
• It’s critical to read the Class 9 Science case study material thoroughly once you’ve grasped the question. This will provide you with a thorough understanding of the problem as well as the various potential solutions.
• Brainstorming potential solutions with classmates or other students might also be beneficial. This might provide you with multiple viewpoints on the situation and assist you in determining the best solution.
• Finally, make sure your answer is presented simply and concisely. Make sure you clarify your rationale and back up your claim with evidence.

A look at the Class 9 Science Syllabus

The CBSE class 9 science syllabus provides a strong foundation for students who want to pursue a career in science. The topics are chosen in such a way that they build on the concepts learned in the previous classes and provide a strong foundation for further studies in science. The table below lists the topics covered in the Class 9 Science syllabus of the Central Board of Secondary Education (CBSE). As can be seen, the Class 9 science syllabus is divided into three sections: Physics, Chemistry and Biology. Each section contains a number of topics that Class 9 science students must study during the course.

CBSE Class 9 Science (Code No. 086)

Theme: Materials Unit I: Matter-Nature and Behaviour Definition of matter; solid, liquid and gas; characteristics – shape, volume, density; change of state-melting (absorption of heat), freezing, evaporation (cooling by evaporation), condensation, sublimation. Nature of matter:  Elements, compounds and mixtures. Heterogeneous and homogenous mixtures, colloids and suspensions. Particle nature and their basic units:  Atoms and molecules, Law of constant proportions, Atomic and molecular masses. Mole concept: Relationship of mole to mass of the particles and numbers. Structure of atoms:  Electrons, protons and neutrons, valency, the chemical formula of common compounds. Isotopes and Isobars.

Theme: The World of the Living Unit II: Organization in the Living World Cell – Basic Unit of life:  Cell as a basic unit of life; prokaryotic and eukaryotic cells, multicellular organisms; cell membrane and cell wall, cell organelles and cell inclusions; chloroplast, mitochondria, vacuoles, endoplasmic reticulum, Golgi apparatus; nucleus, chromosomes – basic structure, number. Tissues, Organs, Organ System, Organism: Structure and functions of animal and plant tissues (only four types of tissues in animals; Meristematic and Permanent tissues in plants).

Theme: Moving Things, People and Ideas Unit III: Motion, Force and Work Motion:  Distance and displacement, velocity; uniform and non-uniform motion along a straight line; acceleration, distance-time and velocity-time graphs for uniform motion and uniformly accelerated motion, derivation of equations of motion by graphical method; elementary idea of uniform circular motion. Force and Newton’s laws:  Force and Motion, Newton’s Laws of Motion, Action and Reaction forces, Inertia of a body, Inertia and mass, Momentum, Force and Acceleration. Elementary idea of conservation of Momentum. Gravitation:  Gravitation; Universal Law of Gravitation, Force of Gravitation of the earth (gravity), Acceleration due to Gravity; Mass and Weight; Free fall. Floatation:  Thrust and Pressure. Archimedes’ Principle; Buoyancy. Work, energy and power:  Work done by a Force, Energy, power; Kinetic and Potential energy; Law of conservation of energy. Sound:  Nature of sound and its propagation in various media, speed of sound, range of hearing in humans; ultrasound; reflection of sound; echo.

Theme: Food Unit IV: Food Production Plant and animal breeding and selection for quality improvement and management; Use of fertilizers and manures; Protection from pests and diseases; Organic farming.

PRESCRIBED BOOKS:

• Science-Textbook for class IX-NCERT Publication
• Assessment of Practical Skills in Science-Class IX – CBSE Publication
• Laboratory Manual-Science-Class IX, NCERT Publication
• Exemplar Problems Class IX – NCERT Publication

myCBSEguide: A true helper

There are numerous advantages to using myCBSEguide to achieve the highest results in Class 9 Science.

• myCBSEguide offers high-quality study materials that cover all of the topics in the Class 9 Science curriculum.
• myCBSEguide provides practice questions and mock examinations to assist students in the best possible preparation for their exams.
• On our myCBSEguide app, you’ll find a variety of solved Class 9 Science case study questions covering a variety of topics and concepts. These case studies are intended to help you understand how certain principles are applied in real-world settings
• myCBSEguide is that the study material and practice problems are developed by a team of specialists who are always accessible to assist students with any questions they may have. As a result, students may be confident that they will receive the finest possible assistance and support when studying for their exams.

So, if you’re seeking the most effective strategy to study for your Class 9 Science examinations, myCBSEguide is the place to go!

Test Generator

Create question paper PDF and online tests with your own name & logo in minutes.

Question Bank, Mock Tests, Exam Papers, NCERT Solutions, Sample Papers, Notes

Related Posts

• Competency Based Learning in CBSE Schools
• Class 11 Physical Education Case Study Questions
• Class 11 Sociology Case Study Questions
• Class 12 Applied Mathematics Case Study Questions
• Class 11 Applied Mathematics Case Study Questions
• Class 11 Mathematics Case Study Questions
• Class 11 Biology Case Study Questions
• Class 12 Physical Education Case Study Questions

Leave a Comment

Save my name, email, and website in this browser for the next time I comment.

• Bihar Board

SRM University

• TN Board Result 2024
• GSEB Board Result 2024
• Karnataka Board Result 2024
• CG Board Result 2024
• Kerala Board Result 2024
• Shiv Khera Special
• Education News
• Web Stories
• Current Affairs
• नए भारत का नया उत्तर प्रदेश
• CBSE Board Result 2024
• School & Boards
• College Admission
• Govt Jobs Alert & Prep
• GK & Aptitude
• CBSE Class 9 Study Material

CBSE Class 9 Science Important Case Study Questions with Answers for Term 2 Exam 2022 (PDF)

Check important case study questions of cbse class 9 science to prepare for the cbse term 2 exam 2022. all these questions have been put together by subject experts..

CBSE Class 9 Term 2 Exam 2022:  Important case based questions for CBSE Class 9 Science are provided here students to prepare for the upcoming Term 2 Exam 2022. All the questions provided below are curated by the subject experts. These questions are really helpful to revise important concepts and prepare the case study questions for the exam. Answers to all questions have been provided for reference. So, students should practice the chapter-wise questions to clearly understand the right way to attempt the case based questions. Download the chapter-wise questions in PDF.

Check some of the important case study questions below:

Q. Read the following and answer the questions :

A student was asked by his teacher to verify the law of conservation of mass in the laboratory. He prepared 5% aqueous solutions of NaCl and Na 2 SO 4 . He mixed 10 mL of both these solutions in a conical flask. He weighed the flask on a balance. He then stirred the flask with a rod and weighed it after sometime. There was no change in mass.

• Was the student able to verify the law of conservation of mass?
• If not, what was the mistake committed by him?
• In your opinion, what he should have done?
• What is the molar mass of Na 2 SO 4 ?
• No, he could not verify the law of conservation of mass in-spite of the fact that there was no change in mass.
• No chemical reaction takes place between NaCl and Na 2 SO 4 . This means that no reaction actually took place in the flask.
• He should have performed the experiment by using aqueous solutions of BaCl 2 and Na 2 SO 4 . A chemical reaction takes place in this case and a white precipitate of BaSO 4 is formed.
• Will the weight of the precipitate be the same as that of the reactants before mixing?
• If not, what she should have done?
• Which law of chemical combination does this support?
• State the law of conservation of mass.
• No, it will not be the same.
• She should have weighed the total contents of the beaker after the reaction and not the precipitate alone.
• It supports the law of conservation of mass.
• Mass can neither be created nor destroyed during a chemical reaction.

Get here latest School , CBSE and Govt Jobs notification in English and Hindi for Sarkari Naukari and Sarkari Result . Download the Jagran Josh Sarkari Naukri App . Check  Board Result 2024  for Class 10 and Class 12 like  CBSE Board Result ,  UP Board Result ,  Bihar Board Result ,  MP Board Result ,  Rajasthan Board Result  and Other States Boards.

• CBSE 12th Result 2024
• manresults.nic.in Result 2024
• results.cbse.nic.in Result 2024
• Digilocker CBSE Board Result 2024
• CBSE 10th Result 2024
• CBSE Result 2024 Digilocker
• CBSE Board 12th Results 2024
• CBSE Board Class 10 Result 2024
• CBSE Study Material
• CBSE Class 9

Latest Education News

MBSE 10th Result 2024: Mizoram Board HSLC Result Date And Time at mbse.edu.in

Mizoram Board Result 2024: MBSE HSLC, HSSLC Result Date And Time At mbse.edu.in

11th Result 2024 Tamil Nadu: Check TN HSE(+1) Class XIth Std Results with Registration Number and Date of Birth

Today’s IPL Match (14 May) - LSG vs DC: Team Squad, Match Time, Where to Watch Live and Stadium

[Today] IPL 2024 Points Table: Team Rankings and Net Run Rate

IPL Playoffs 2024: Teams Scenario, Qualifier, Eliminator Rules, Venues and Other Details

Who Won Yesterday IPL Match: KKR vs GT, Match 63, Check All Details and Latest Points Table

TN 11th Result 2024 Live Updates: Check Tamil Nadu TNDGE HSE(+1) Results Online Today at 9:30 AM at tnresults.nic.in With Registration Number and DOB

CBSE 10th Result 2024 LIVE: cbseresults.nic.in Class 10 Result at Official Website, Check Online with Roll Number and Toppers Details

MBSE HSLC Result 2024 LIVE Updates: Check Mizoram Class 10 Results Online at Official Website - mbse.edu.in by Roll, Registration Number

SSC GD 2024 Result Live Update: Official Website to Download the Constable Results ssc.gov.in, Check Merit List Date, Latest Updates

Brainteaser: Can You Find the Missing Zero? A Number Puzzle that Will Trick Your Eyes

Introducing a Hybrid Pitch: What kind of pitch is this in cricket?

MPPSC Assistant Professor Syllabus 2024: PDF Download for Subject-Wise Topics, Check Exam Pattern

CBSE Board Result 2024 Released, What Next? Check Psychological and Tele-Counseling with Centralized Toll Free Number

Optical Illusion Eye Test: Find the leopard in the picture in 3 seconds!

भारत की शास्त्रीय भाषाओं की सूची, यहां पढ़ें

CBSE Board Result 2024 Analysis: Check District-wise Pass Percentage, Foreigner's Students Stats, Marks and Topper's Details

CBSE Board Result 2024 Class 10 Declared LIVE: Check Official Link: cbseresults.nic.in, CBSE Board 10th Results Announced on Umang and Digilocker Apps by Roll Number, Date of Birth

COHSEM Result 2024 Declared: Check Manipur Class 12 Results at manresults.nic.in with Roll Number, Check Topper List

NCERT Solutions for Class 9 Science Chapter 4 Structure of the Atom

NCERT Solutions for Class 9 Science Chapter 4 Structure of the Atom in Hindi and English Medium prepared for new session 2024-25. Class 9 Science chapter 4 is modified and revised as per the new rationalised NCERT textbooks issued for academic year 2024-25.

Class 9 Science Chapter 4 Question Answers

• Class 9 Science Chapter 4 Exercises
• Class 9 Science Chapter 4 Intext Questions
• Class 9 Science Chapter 4 Extra Questions
• Class 9 Science Chapter 4 Hindi Medium
• Class 9 Science Chapter 4 Notes in English
• Class 9 Science Chapter 4 Notes in Hindi
• Class 9 Science Chapter 4 NCERT Book
• Class 9 Science NCERT Solutions
• Class 9 all Subjects NCERT Solutions

NCERT Class 9 Science textbook, Chapter 4 Structure of the Atom delves into the structure and components of atoms, providing insight into the fundamental building blocks of matter. The main topics covered in Chapter 4 are the concept of the atom as the basic unit of matter, Dalton’s Atomic Theory that is a brief overview of Dalton’s atomic theory and its postulates. Here we will study about Charged Particles in Matter which provides the explanation of charged particles in matter, including electrons, protons, and neutrons.

Distribution of Electrons in Different Orbits (Shells) Class 9 students learn in chapter 4 about explanation of electron distribution in shells or energy levels and introduction to the K, L, M, and N shells. It also explains the definition of valency and its significance, determining valency based on electron distribution. Here, we learn about Atomic Number and Mass Number with explanation of atomic number and its significance, definition of mass number and how it is determined. Class 9 science chapter 4 explores about the definition of isotopes and examples, explanation of isotopic notation.

A recap of the main concepts and ideas presented in Chapter 4 Structure of the Atom, provides a foundational understanding of the structure and components of atoms. It introduces students to the historical development of atomic models and sets the stage for further exploration of atomic and molecular structures in subsequent chapters and classes.

Preparing for NCERT Class 9 Science Chapter 4 Structure of the Atom, requires a proper approach to understanding the fundamental concepts related to atomic structure. Here are some steps and planning strategies for students to prepare this chapter 4 of 9th science effectively. First of all, read the Chapter Thoroughly, begin by reading the chapter carefully from the NCERT textbook. Pay attention to definitions, examples, and key points. While reading, take detailed notes on important concepts, definitions, and key terms.

To make science easy, summarize the main ideas of each section. Understand the historical development of atomic models, including Dalton’s atomic theory, J.J. Thomson’s experiments, Rutherford’s gold foil experiment, and Bohr’s model. Know the key contributions of these scientists. Study the components of an atom, including electrons, protons, and neutrons. Understand their properties, locations, and charges. Learn about Bohr’s model of the hydrogen atom, including the concept of energy levels or orbits and how it explains spectral lines.

Class IX Science chapter 4 Exercise and Intext question answers in PDF format to free download. Class 9 UP Board students also get here UP Board Solutions. Class 9 Science chapter 4 Intext questions given on Page 43 or Page 49 or Page 50 or Page 52 or Page 53 and Exercises in English Medium are available.

You can download these solutions from Page 53 ke Uttar or Page 56 ke Uttar or Page 57 ke Uttar or Page 58 ke uttar or Page 59 ke Uttar or Page 60 ke Uttar and Abhyaas ke Uttar to study online or in PDF file format. NCERT Solutions and Offline Apps for all other subjects based on latest CBSE Syllabus are also available to download.

Electron Distribution and Valency Understand how electrons are distributed in different shells or energy levels (K, L, M, N). Learn the maximum number of electrons each shell can hold. Know the definition of valency and how it relates to electron distribution. Practice determining the valency of elements based on their electron configuration. Learn how to calculate the number of protons, electrons, and neutrons in an atom. Isotopes: Understand isotopic notation.

Practice solving numerical problems related to atomic structure, atomic number, mass number, and electron distribution. Work through exercises and examples in the textbook. Utilize diagrams and visual aids in the chapter to help understand atomic structures and models. Supplement your learning with online resources, videos, and interactive simulations related to atomic structure. These can provide additional clarity. Group study can offer different perspectives and help reinforce your understanding.

Regularly revise your notes and the key points of the chapter 4 in 9th science. Repetition is key to retaining information. Closer to your exams, practice solving sample papers and previous year’s question papers to familiarize yourself with the exam pattern and practice time management. If you have doubts or find certain topics challenging, don’t hesitate to seek help from your teacher or classmates. Clarify your doubts as soon as possible. By following these planning strategies and staying organized, you can effectively prepare for NCERT Class 9 Science Chapter 4 and build a strong foundation in atomic structure and chemistry concepts.

Extra Questions on 9th Science Chapter 4

Is atomic number of an atom always equal to the number of electrons.

No, it is the case when the atom has no charge. In case of cation (positively charged), atomic number is more than the number of electrons and in case of anion (negatively charged), it is less than the number of electrons.

Nucleus of an atom has positive charge on it. Establish.

This can be established on the basis of Rutherford scattering experiment. Since some alpha particles were repelled by the nucleus of the atom, it is expected to have the same charge as on alpha particles. Therefore, nucleus of an atom has positive charge.

Were neutrons known at the time Rutherford performed the scattering experiment?

No, these were discovered later on by Chadwick in 1931 whereas scattering experiment was performed by Rutherford in 1911.

Why are isotopes of an element chemically similar?

Isotopes of an elements have same number of electrons and therefore, same value shell electronic distribution. Since the chemical properties of the atoms are related to valence shell configurations, the isotopes are chemically similar.

Why do elements which exist as isotopes have fractional atomic masses?

The different isotopes of an element differ in their mass number as well as atomic masses. In order to represent the atomic mass of the element, we have to consider average of the atomic masses of the different isotopes and also the ratio in which these are present. In most of the cases, the average comes out to be in fraction. Therefore, these elements have fractional atomic masses.

Why is a proton not a universal particle like electron?

A proton is the positively charged residue left when hydrogen gas is enclosed in the in the discharge tube. For the other gases, the positive residues formed contain different number of protons. Therefore, proton is not a universal particle like electron.

Tiwari Academy plays a significant role in helping students prepare for NCERT Class 9 Science Chapter 4. Here’s how Tiwari Academy can assist students in their preparation for this chapter. It provides detailed solutions to all the questions and exercises in the NCERT Class 9 Science textbook for Chapter 4. These solutions can help students understand how to approach and solve different types of problems related to the structure of atoms.

Important Questions on 9th Science Chapter 4

What are the limitations of j.j. thomson’s model of the atom.

According to J.J. Thomson’s model of an atom, an atom consists of a positively charged sphere with electrons embedded in it. However, it was later found that the positively charged particles reside at the center of the atom called the nucleus, and the electrons revolve around the nucleus.

What are the limitations of Rutherford’s model of the atom?

According to Rutherford’s model of an atom, electrons revolve around the nucleus in fixed orbits. But, an electron revolving in circular orbits will not be stable because during revolution, it will experience acceleration. Due to acceleration, the electrons will lose energy in the form of radiation and fall into the nucleus. In such a case, the atom would be highly unstable and collapse.

Define valency by taking examples of silicon and oxygen.

The valency of an element is the combining capacity of that element. The valency of an element is determined by the number of valence electrons present in the atom of that element. If the number of valence electrons of the atom of an element is less than or equal to four, then the valency of that element is equal to the number of valence electrons. For example, the atom of silicon has four valence electrons. Thus, the valency of silicon is four. On the other hand, if the number of valence electrons of the atom of an element is greater than four, then the valency of that element is obtained by subtracting the number of valence electrons from eight. For example, the atom of oxygen has six valence electrons. Thus, the valency of oxygen is (8 − 6) i.e., two.

Explain Atomic number with examples.

Atomic number: The atomic number of an element is the total number of protons present in the atom of that element. For example, nitrogen has 7 protons in its atom. Thus, the atomic number of nitrogen is 7.

What do you understand by isobars?

Isobars: They are atoms of different elements having same mass number but different atomic number. For example calcium, atomic number 20 and argon, atomic number 18. The number of electrons in these atoms is different, but the mass number of both these elements is 40. That is, the total number of neutrons is the same in the atoms of this pair of elements.

If Z = 3, what would be the valency of the element? Also, name the element.

By Z = 3, we mean that the atomic number of the element is 3. Its electronic configuration is 2, 1. Hence, the valency of the element is 1 (since the outermost shell has only one electron). Therefore, the element with Z = 3 is lithium.

NCERT Solutions for Class 9 Science Chapter 4 Structure of the Atom Intext Questions and chapter end exercise question answers are given below to free download. All the solutions are free to download without any registrations or login. We have updated all the contents on the basis of user’s suggestions and Feedback received from last academic session.

The Tiwari Academy website and apps offer explanations and videos that break down complex concepts in the chapter. Visual aids and clear explanations can help students grasp difficult topics more easily. It also provide historical context and explanations for the development of atomic models, making it easier for students to understand the evolution of atomic theory. The platform offer visual representations and interactive simulations of atomic structures, which can enhance students’ understanding of the arrangement of electrons, protons, and neutrons within an atom.

Questions related to class 9 science chapter 4, atomic structure and atomic models are frequently included in Class 9 Science examinations. Students can expect to see questions about atomic components, electron distribution, atomic number, and mass number in their exams. The chapter covers the historical development of atomic models, including Dalton’s atomic theory, J.J. Thomson’s experiments, Rutherford’s gold foil experiment, and Bohr’s model. Understanding the history of atomic theory is often tested in exams.

Question 1: An electron is regarded as a universal particle. Explain. Answer 1: The value of charge (e) and mass (m) of the electron always remain the same whatever may be the source of their emission. In the discharge tube, the electrons may be emitted either from the cathode or form the gas enclosed in the discharge tube. Whatever may be the metal which forms the cathode or the gas present in the discharge tube, these values remain the same. Therefore, electron is regarded as a universal particle.

Question 2: Why do the element helium, neon and argon have zero valency? Answer 2: Helium has two electrons in its only energy shell (K-shell). The other two elements have eight electrons in their valence shells. Since these are the maximum number of electrons which the atoms of these elements can have therefore, they do not have any urge or desire to take part in chemical combination. These elements are known as zero valent elements. They have therefore, valency equal to zero.

Class 9 Science chapter 4 bridges the gap between chemistry and physics by introducing concepts related to atomic structure. It sets the stage for students to explore topics like the periodic table, chemical bonding, and atomic physics in later classes. Knowledge of atomic structure is relevant to various scientific fields, including chemistry, physics, and materials science. Exams include questions that require students to apply their understanding of atomic structure to real-world scenarios. A strong foundation in Chapter 4 is, therefore, essential for success in future science studies.

Finally, the NCERT Class 9 Science Chapter 4, Structure of the Atom, is important not only for scoring well in exams but also for laying the groundwork for a deeper understanding of chemistry and physics concepts. Students should dedicate time and effort to comprehensively learn the concepts presented in this chapter to ensure success in their science studies.

« NCERT Solutions Class 9 Science Chapter 3

Ncert solutions class 9 science chapter 5 ».

Copyright 2024 by Tiwari Academy | A step towards Free Education

NCERT Solutions for Class 9 Science Chapter 4 Structure of the Atom

• 23rd December 2023

NCERT Solutions for Class 9 Science (Chemistry) Chapter 4 Structure of the Atom provides detailed answers for all in-text and exercise Questions. These solutions contain an in-depth explanation of each topic involved in the chapter. All these solutions are prepared by expert teachers and updated for the current academic session.

NCERT Solutions for Class 9 Science (Chemistry) Chapter 4 Structure of the Atom Pure help students to understand the fundamental concepts given in class 9 Science textbook. We have prepared the answers to all the questions in an easy and well-structured manner. It helps students to grasp the chapter easily.

CBSE Class 9 Science Structure of the Atom Intext Questions (Solved)

PAGE NO – 39

Question 1: What are canal rays?

Answer: Canal rays are positively charged radiations. These rays consist of positively charged particles known as protons. They were discovered by Goldstein in 1886.

Question 2: If an atom contains one electron and one proton, will it carry any charge or not?

Answer: If an atom contains one electron and one proton, it will not carry any net charge. This is because a proton has a positive charge and an electron has a negative charge, and these two charges are equal in magnitude but opposite in sign. In such an atom, the positive charge of the proton and the negative charge of the electron will cancel each other out, resulting in a neutral overall charge. An example of such an atom is hydrogen, which typically has one proton and one electron in its most common form.

PAGE NO. 41

Question 1: On the basis of Thomson’s model of an atom, explain how the atom is neutral as a whole.

Answer: According to Thomson’s model of the atom, an atom consists of both negatively and positively charged particles. The negatively charged particles are embedded in the positively charged sphere. These negative and positive charges are equal in magnitude. Thus, by counterbalancing each other’s effect, they make an atom neutral.

According to Thomson’s model, an atom is neutral because it contains an equal amount of positive and negative charges that balance each other out. In this model, the atom is like a positively charged sphere with negatively charged electrons embedded in it. The positive charge is spread out over the entire sphere, and the electrons are placed within this sphere. Since the number of negative charges (electrons) equals the number of positive charges in the sphere, the overall charge of the atom is neutral. This balance of equal and opposite charges ensures that the atom does not have a net charge.

Question 2: On the basis of Rutherford’s model of an atom, which subatomic particle is present in the nucleus of an atom?

Answer: On the basis of Rutherford’s model of an atom, protons (positively-charged particles) are present in the nucleus of an atom.

Question 3: Draw a sketch of Bohr’s model of an atom with three shells.

Question 4: What do you think would be the observation if the α-particle scattering experiment is carried out using a foil of a metal other than gold?

Answer: If the α-scattering experiment is carried out using a foil of metal rather than gold, there would be no change in the observation. In the α-scattering experiment, a gold foil was taken because gold is malleable and a thin foil of gold can be easily made. It is difficult to make such foils from other metals.

Question 1: Name the three sub-atomic particles of an atom.

Answer: The three sub-atomic particles of an atom are:

• Protons   
• Electrons, and

Question 2: Helium atom has an atomic mass of 4 u and two protons in its nucleus. How many neutrons does it have?

Answer: Helium atom has two neutrons. The mass of an atom is the sum of the masses of protons and neutrons present in its nucleus. 

Since helium atom has two protons, mass contributed by the two protons is (2 × 1) u = 2 u. Then, the remaining mass (4 − 2) u = 2 u is contributed by 2u /1u = 2 neutrons.

PAGE NO. 42

Question 1: Write the distribution of electrons in carbon and sodium atoms?

Answer: The total number of electrons in a carbon atom is 6. The distribution of electrons in carbon atom is given by: 

Or,  we can write the distribution of electrons in a carbon atom as 2, 4. The total number of electrons in a sodium atom is 11. The distribution of electrons in sodium atom is given by: 

Or,  we can write distribution of electrons in a sodium atom as 2, 8, 1.

Question 2: If K and L shells of an atom are full, then what would be the total number of electrons in the atom?

Answer: The maximum number of electrons that can occupy K and L-shells of an atom are 2 and 8 respectively. Therefore, if K and L-shells of an atom are full, then the total number of electrons in the atom would be (2 + 8) = 10 electrons.

PAGE NO. 43

Question 1: How will you find the valency of chlorine, sulphur and magnesium?

Answer: If the number of electrons in the outermost shell of the atom of an element is less than or equal to 4, then the valency of the element is equal to the number of electrons in the outermost shell. 

On the other hand, if the number of electrons in the outermost shell of the atom of an element is greater than 4, then the valency of that element is determined by subtracting the number of electrons in the outermost shell from 8. 

The distribution of electrons in chlorine, sulphur, and magnesium atoms are 2, 8, 7; 2, 8, 6 and 2, 8, 2 respectively. Therefore, the number of electrons in the outermost shell of chlorine, sulphur, and magnesium atoms are 7, 6, and 2 respectively. 

Thus, The valency of chlorine = 8 −7 = 1 The valency of sulphur = 8 − 6 = 2 The valency of magnesium = 2

Question 1: If number of electrons in an atom is 8 and number of protons is also 8, then  (i) what is the atomic number of the atom and  (ii) what is the charge on the atom?

Answer: (i) The atomic number is equal to the number of protons. Therefore, the atomic number of the atom is 8.

(ii) Since the number of both electrons and protons is equal, therefore, the charge on the atom is 0.

Question 2:  With the help of Table 4.1, find out the mass number of oxygen and sulphur atom.

Answer: Mass number of oxygen = Number of protons + Number of neutrons = 8 + 8 = 16

 Mass number of sulphur = Number of protons + Number of neutrons = 16 +16 = 32

PAGE NO. 45

Question 1: For the symbol H, D and T tabulate three sub – atomic particles found each of them.

Question 2: Write the electronic configuration of any pair of isotopes and isobars.

Answer: Isotopes: Isotopes are atoms which have the same number of protons but the number of neutrons differs. This leads to the variation in mass number too.

Two isotopes of carbon are 6 𝐶 12 and 6 𝐶 14 The electronic configuration of 6 𝐶 12 is 2, 4. The electronic configuration of 6 𝐶 14 is 2, 4. [Isotopes have same electronic configuration]

Isobars: Isobars are atoms which have the same mass number but differ in the atomic number. Electronic configuration of an isobar pair is as follows,

29 Ca 40 and 8 𝐴𝑟 40 are a pair of isobars of calcium. The electronic configuration of 29 Ca 40 is 2, 8, 8, 2 The electronic configuration of 18 𝐴𝑟 40 is 2, 8, 8.  [Isobars have different electronic configuration]

NCERT Class 9 Science Structure of the Atom Exercise Questions (Solved)

Question 1: Compare the properties of electrons, protons and neutrons. 

Question 2: What are the limitations of J.J. Thomson’s model of the atom?

Answer: J.J. Thomson’s model of the atom, known as the “plum pudding model,” had a few key limitations:

1. According to J.J. Thomson’s model of an atom, an atom consists of a positively charged sphere with electrons embedded in it. However, later Rutherford’s gold foil experiment showed that the positively charged particles reside at the center of the atom called the nucleus, and the electrons revolve around the nucleus.

2. Thomson’s model was unable to explain many chemical properties of elements, such as why atoms combine in fixed ratios to form compounds.

3. It didn’t clearly distinguish between the nucleus and the rest of the atom, and couldn’t explain why atoms are stable.

Question 3: What are the limitations of Rutherford’s model of the atom?

Answer: According to Rutherford’s model of an atom, electrons revolve around the nucleus in fixed orbits. But, an electron revolving in circular orbits will not be stable because, during the revolution, it will experience acceleration. Due to acceleration, the electrons will lose energy in the form of radiation and fall into the nucleus. In such a case, the atom would be highly unstable and collapse.

Question 4: Describe Bohr’s model of the atom.

Answer: Bohr’s model of the atom Niels Bohr proposed the following postulates regarding the model of the atom.

• Only certain orbits known as discrete orbits of electrons are allowed inside the atom.
• While revolving in these discrete orbits, the electrons do not radiate energy. These discrete orbits or shells are shown in the following diagram.

The first orbit (i.e., for n = 1) is represented by letter K.  Similarly, for n = 2, it is L − shell, for n = 3, it is M − shell and for n = 4, it is N − shell. These orbits or shells are also called energy levels.

Question 5: Compare all the proposed models of an atom given in this chapter.

Question 6: Summarize the rules for writing of distribution of electrons in various shells for the first eighteen elements.

Answer: The  rules  for  writing  of   the  distribution  of  electrons   in   various   shells   for  the first   eighteen  elements are given below:

(i) The maximum number of electrons that a shell can accommodate is given by the formula ‘2n 2 ‘, where ‘n’ is the orbit number or energy level index (n = 1, 2, 3…). Now, Maximum number of electrons in different shells are: K shell n = 1: 2n 2  = 2(1) 2  = 2 L shell n = 2: 2n 2  = 2(2) 2  = 8 M shell n = 3: 2n 2  = 2(3) 2  = 18 N shell n = 4: 2n 2  = 2(4) 2  = 32

(ii) The outermost orbit can be accommodated by a maximum number of 8 electrons.

(iii) Shells are filled with electrons in a step-wise manner i.e., the outer shell is not occupied with electrons unless the inner shells are completely filled with electrons.

Question 7: Define valency by taking examples of silicon and oxygen.

Answer: Valency is the measure of the ability of an atom to combine with other atoms. It is determined by the number of electrons an atom can lose, gain, or share to become stable.

• Example with Silicon : Silicon has 4 electrons in its outermost shell. It can share these 4 electrons with other atoms to complete its outer shell, typically holding 8 electrons. So, the valency of silicon is 4, as it can form bonds by sharing 4 electrons.
• Example with Oxygen : Oxygen has 6 electrons in its outer shell. It needs 2 more electrons to complete its shell. So, it can either gain 2 electrons or share 2 electrons with other atoms. Therefore, the valency of oxygen is 2.

Question 8. Explain with examples: (i) Atomic number (ii) Mass number, (iii) Isotopes and (iv) Isobars. Give any two uses of isotopes.

(i) Atomic number: The atomic number of an element is the total number of protons present in the atom of that element. For example, nitrogen has 7 protons in its atom. Thus, the atomic number of nitrogen is 7.

(ii) Mass number: The mass number of an element is the sum of the number of protons and neutrons present in the atom of that element. For example, the atom of boron has 5 protons and 6 neutrons. So, the mass number of boron is 5 + 6 = 11.

(iii) Isotopes: They are atoms of the same element and have same atomic number but different mass number/atomic mass. For example: C 12  and  6 C 14

(iv) Isobars: They are atoms of different elements having same mass number but different atomic number. For example calcium, atomic number 20 and argon, atomic number 18. The number of electrons in these atoms is different, but the mass number of both these elements is 40. That is, the total number of neutrons is the same in the atoms of this pair of elements.

Two uses of isotopes are as follows:

• An isotope of uranium is used as a fuel in nuclear reactors.
• An isotope of cobalt is used in the treatment of cancer.

Question 9: Na has completely filled K and L shells. Explain.

Answer: Na has atomic number 11, so its electronic configuration is = 2, 8, 1 Sodium atom (Na) looses 1 electron to become stable and form Na +  ion. so its electronic configuration is = 10 = 2, 8. The above configuration indicates completely filled K, L shells.

Question 10: If bromine atom is available in the form of, say, two isotopes 35 𝐵𝑟 79 (49.7%) and 35 𝐵𝑟 81 (50.3%), calculate the average atomic mass of bromine atom.

Answer: The average atomic mass of bromine

Question 11. The average atomic mass of a sample of an element X is 16.2 u. What are the percentages of isotopes  16 8 X and  18 8 X in the sample?

Question 12: When 90% is the X-16 sample so for X-18 sample % = 100-90=10% If Z = 3, what would be the valency of the element? Also, name the element.

Answer: By   Z = 3, we mean that the atomic number of the element is 3. Its electronic configuration is 2, 1. Hence, the valency of the element is 1 (since the outermost shell has only one electron). Therefore, the element with Z = 3 is lithium.

Question 13: Composition of the nuclei of two atomic species X and Y are given as under

Give the mass numbers of X and Y. What is the relation between the two species?

Answer: Mass number of    X = Number of protons + Number of neutrons = 6 + 6 = 12

Mass number of    Y = Number of protons + Number of neutrons = 6 + 8 = 14

These two atomic species X and Y have the same atomic number, but different mass numbers. Hence, they are isotopes.

Question 14. For the following statements, write T for true and F for false. (a) J.J. Thomson proposed that the nucleus of an atom contains only nucleons. (b) A neutron is formed by an electron and a proton combining together. Therefore it is neutral. (c) The mass of an electron is about 1/2000 times that of proton. (d) An isotope of iodine is used for making tincture iodine, which is used as a medicine.

Solution: (a) False (b) False (c) True (d) False

Put a tick(✓) against correct choice and cross(x) against wrong choice in questions 15, 16 and 17.

Question 15. Rutherford’s alpha-particle scattering experiment was responsible for the discovery of (a) Atomic nucleus (b) Electron (c) Proton (d) Neutron

Answer: (a) Atomic nucleus

Question 16. Isotopes of an element have (a) The same physical properties (b) Different chemical properties (c) Different number of neutrons (d) Different atomic numbers.

Answer: (c) Different number of neutrons

Question 17. Number of valence electrons in Cl − ion are: (a) 16 (b) 8 (c) 17 (d) 18

Answer: (b) 8

Electronic distribution of Cl is K-2, L-8, M-7. Valence electrons are 7, hence chlorine gains one electron for the formation of Cl – . Therefore, its valency is 8.

Question 18. Which one of the following is a correct electronic configuration of Sodium? (a) 2, 8 (b) 8, 2, 1 (c) 2, 1, 8 (d) 2, 8, 1

Answer: (d) 2, 8, 1

Question 19: Complete the following table.

Answer: The following table depicts the missing data: Atomic number(Z) =Number of protons Mass number = Number of neutrons + atomic number (or) Mass number(A) = Number of neutrons + number of neutrons

Leave a Reply Cancel Reply

Your email address will not be published. Required fields are marked *

Name  *

Email  *

Add Comment  *

Post Comment

Talk to our experts

1800-120-456-456

• Important Questions for CBSE Class 9 Science Chapter 4 - Structure of the Atom

CBSE Class 9 Science Chapter-4 Important Questions - Free PDF Download

Important Questions for Class 9 Science Chapter 4 the structure of the atom is created by subject matter experts at Vedantu. The main concept behind creating the important questions for the chapter to enable students to prioritize the concepts of chapter introduced in Science Class 9. The important questions of structure of atom Class 9 are prepared to give a better conceptual understanding. With the help of Class 9 Science Chapter 4 important questions, it would be easy to assume the type of questions will be asked in the chapter exam. The language used while preparing the important questions is proficient and understandable by a Class 9 student. Vedantu is a platform that provides free CBSE Solutions (NCERT) and other study materials for students. Maths and Science Students who are looking for the better solutions ,they can download Class 9 Maths NCERT Solutions and Class 9 Science NCERT Solutions to help you to revise complete syllabus and score more marks in your examinations.

Download CBSE Class 9 Science Important Questions 2024-25 PDF

Also, check CBSE Class 9 Science Important Questions for other chapters:

Important Topics Covered In Class 9 Science Chapter 4 - Structure of the Atom

The following is a list of some of the important topics and subtopics that students will come across while studying Chapter 4 - Structure of the Atom. Students are advised to ensure that they have covered all these topics while preparing for the exam as questions are likely to be asked from them.

Introduction

Charged Particles In Matter

The Structure of An Atom

The Thomson's Model of An Atom

Rutherford's Model of An Atom

Drawbacks of Rutherford's Model of An Atom

Bohr’s Model of An Atom

How Are Electrons Distributed In Different Orbits?

Atomic Number And Mass Numbers

Study Important Questions for Class 9 Science Chapter 4 – Structure of Atoms

Very short answer questions (1 mark).

1. What are canal rays?

Ans: Positively charged rays discovered by E. Goldstein are called canal rays.

2. If an atom contains one electron and one proton, will it carry any charge or not?

Ans: A single electron contains one negative charge and one single proton contains one positive charge so they are neutralized by each other. That atom will not contain any charge.

3. Name the three sub-atomic particles of an atom.

Ans: Three subatomic particles of an atom are Proton, Neutron and Electron.

4. Rutherford’s alpha-particle scattering experiment was responsible for the discovery of

 Atomic Nucleus

 Electron

 Proton 

 Neutron

Ans: (d) Proton

5. Isotopes of an element have

 The same physical properties

 Different chemical properties

 Different number of neutrons

 Different atomic numbers

Ans: (a) The same physical properties.

6. Number of valence electrons in $C{{l}^{-}}$ ion are:

7. Which one of the following is a correct electronic configuration of sodium?

 8,2,1

 2,1,8

 2,8,1

Ans : (b) 2,8

8. Atomic Number of an element is equal to:

 Number of Protons

 Number of electrons

 Number of neutrons

 Both (a) and (b)

Ans: (a) Number of Protons

9. The charge of proton $({{p}^{+}})$ is:

$+1.6\times {{10}^{-19}}C$ 

$-1.6\times {{10}^{-19}}C$

$+1.6\times {{10}^{19}}C$

$-1.6\times {{10}^{19}}C$

Ans : (a) $+1.6\times {{10}^{-19}}C$

 10. ${}_{10}^{20}Ne$ and ${}_{10}^{22}Ne$ are

 Isotopes

 Isobars

 Isotones

Ans: (a) Isotopes

 11. Helium $\left( {}_{2}^{4}He \right)$ has:

 $2P+$ and $2n{}^\circ $

 $2P+$ and $4n{}^\circ $

 $4P+$ and $2n{}^\circ $

Ans: (a) $2P+$ and $2n{}^\circ $

 12. In which form is oxygen available?

 ${{O}^{2-}}$ 

 ${{O}^{2+}}$

 Both (a) and (c)

Ans: (a) ${{O}^{2+}}$

 13. How many electrons does $N{{a}^{+}}$ has in its outermost shell?

Ans: (d) 8 

 14. Atomic number of an element during a Chemical reaction.

 Increases

 Remain Constant

 Decreases

 May be (a) or (c)

Ans: (b) Remain constant

 15. The molecular formula for Aluminum chloride is 

 $A{{l}_{3}}Cl$

 $AlC{{l}_{3}}$

 $AlC{{l}_{3}}$ 

 Both (b) and (c)

Ans: (c) $AlC{{l}_{3}}$

 16. Atomicity of fluorine is:

Ans : (b) 2

 17. Molecular formula for calcium fluoride is-

$Ca{{F}_{2}}$ 

 $CaF$

 $C{{a}_{2}}F$

 $2CaF$

Ans: (a) $Ca{{F}_{2}}$

 18. Electronic configuration of calcium is

 2,8,8,2

 2,8,6,4

 2,8,7,1

 2,8,1,7

Ans: (a) 2,8,8,2

  19. Nitrogen is:

 Monatomic

 Diatomic

 Triatomic

 Tetratomic

Ans: (b) Diatomic

Short Answer Question (2 Marks)

1. On the basis of Thomson’s model of an atom, explain how the atom is neutral as a whole.

Ans: As per Thomson’s model of an atom, the number of electrons and the number of protons are equal in an atom. Electrons are positively charged and protons are negatively charged, hence the + and – charges are neutralized by each other that makes atoms neutral as a whole.

2. On the basis of Rutherford’s model of an atom, which subatomic particle is present in the nucleus of an atom?

Ans: The subatomic particle proton is present in the nucleus of an atom according to Rutherford’s model of an atom.

3. Draw a sketch of Bohr’s model of an atom with three shells.

Ans: Bohr’s model of an atom with three shells is as follows:

4. What do you think would be the observation if the $\alpha -$ particle scattering experiment is carried out using a foil of a metal other than gold?

Ans : If the $\alpha -$ particle scattering experiment is carried out using a foil of a metal other than gold we will get a different observation. 

5. Helium atom has an atomic mass of 4 u and two protons in its nucleus. How many neutrons does it have?

Ans: The atomic mass of an atom is the sum of masses of protons and neutrons present in its nucleus.

Given that the mass of the helium atom is 4 u and two protons present in its nucleus.

So the number of neutrons will be

$\text{Number of neutrons = atomic mass }-\text{ number of protons}$ 

$\Rightarrow \text{Number of neutrons = 4}-2$

$\therefore \text{Number of neutrons = }2$

Therefore, the helium atom has 2 neutrons.

6. Write the distribution of electrons in carbon and sodium atoms.

Ans: Atomic number of carbon is 6 and the atomic number of sodium is 11.

So distribution of electrons in carbon atom is 6 = 2,4

Distribution of electrons in the sodium atom is 11 = 2,8,1.

7. If K and L shells of an atom are full, then what would be the total number of electrons in the atom?

Ans: K shell contains total 2 electrons and L shell contains maximum 8 electrons. If K and L shells of an atom are full, then the total number of electrons in the atom will be 10.

8. If number of electrons in an atom is 8 and number of protons is also 8, then

What is the atomic number of the atom? 

Ans: The atomic number of an atom is equal to the number of protons or electrons present in its nucleus. So the atomic number of an atom with 8 electrons and 8 protons is 8.

What is the charge on the atom?

Ans: A single electron contains one negative charge and one single proton contains one positive charge. There are equal numbers of electrons and protons in an atom so they neutralize each other. The atom will be neutral.

9. With the help of Table 4.1, find out the mass number of oxygen and Sulphur atoms.

Ans : The mass number of an atom is equal to the sum of protons and neutrons present in its nucleus. 

\[Mass\text{ }number\text{ }of\text{ }oxygen=8+8\] 

\[Mass\text{ }number\text{ }of\text{ }oxygen=16\] 

\[Mass\text{ }number\text{ }of\text{ Sulphur}=16+16\] 

\[Mass\text{ }number\text{ }of\text{ Sulphur}=32\]

10. What are the limitations of J.J. Thomson’s model of the atom?

Ans: The J.J. Thomson’s atomic model failed to explain the organization of electrons in an atom.

11. $N{{a}^{+}}$ has completely filled K and L shells. Explain.

Ans: Sodium $(Na)$ has atomic number 11, so the electronic configuration of $Na$ is 2,8,1.

It has a single electron in the outermost shell, when it gives away that electron it becomes $N{{a}^{+}}$ and has electronic configuration 2,8. Also the K shell contains a total 2 electrons and the L shell contains a maximum of 8 electrons. So $N{{a}^{+}}$ has completely filled K and L shells.

12. If $z=3$, what would be the valency of the element? Also, name the element.

Ans : $z=3$ represents that element has 3 electrons in its shells. The electronic configuration is 2,1. It means the outermost shell electron has 1 electron, so its valency is 1. The element is Lithium.

 Composition of the nuclei of two atomic species X and Y are given as under

13. Give the mass number of X and Y. What is the relation between the two species?

Ans: The mass number of an atom is equal to the sum of protons and neutrons present in its nucleus.

So the mass number of X is $=6+6=12$ 

Mass number of Y is $=6+8=14$ 

Number of protons is the same in X and Y but the atomic numbers are different. X and Y are isotopes.

 For the following statements, write T for True and F for False.

 J.J. Thomson proposed that the nucleus of an atom contains only nucleons.

 A neutron is formed by an electron and a proton combining together. Therefore, it is neutral.

The mass of an electron is about 12000 times that of proton.

 An isotope of iodine is used for making tincture iodine, which is used as a medicine.

14. The nucleus of an atom of Bi – 210 (atomic number = 83) emits $\beta -$ particle and becomes a polonium nuclide. Write as equation for the nuclear change described.

Ans : Whenever a $\beta -$particle emits from the nucleus of an atom, the atomic number of that atom is increased by 1 but the mass number remains the same.

So when a $\beta -$particle emits from Bi – 210 (atomic number = 83) it becomes polonium nuclide. The equation for the nuclear change is as follows:

${}_{83}^{210}Bi\to {}_{84}^{210}Po+{}_{-1}^{0}e$.

16. How can one conclude that electrons are fundamental particles?

Ans: The $\dfrac{e}{m}$ ratio of electrons remains similar irrespective of the nature of gas and electrodes inside the discharge tube. So we can conclude that electrons are fundamental particles.

17. What happens to the nucleus of an atom when it emits a $\gamma -$ ray?

Ans: There is no change in mass or charge of nuclide when it emits $\gamma -$ ray. The energy of the nucleus decreases equal to the energy of photons emitted.

  18. Write the electronic configuration of following ions:

 $C{{l}^{-}}$ 

Ans: Electronic configuration of $C{{l}^{-}}$ ion is 2,8,8.

Ans : Electronic configuration of $Mg$ion is 2,8,2.

 $A{{l}^{3+}}$

Ans : Electronic configuration of $A{{l}^{3+}}$ ion is 2,8.

 $O$ 

Ans: Electronic configuration of $O$ is 2,6.

19. State Mendeleev’s periodic law? 

Ans: Mendeleev’s Periodic law states that the properties of elements are periodic functions of their atomic mass. Properties of elements depend on the atomic mass.

20. Define ionization energy and electron affinity?

Ans : Ionization energy of a component is that the amount of energy that has got to be supplied to at least one mole of the element within the gaseous state to get one mole of caters within the gaseous state.

Electron affinity point is that the energy change that accompanies the formation of 1 mole of anions within the gaseous state from one mole of the atoms of the element within the gaseous state.

21. Why is atomic number is more important than atomic weight in predicting the chemical properties of elements?

Ans: Atomic number is that the number of protons in an atom and through a reaction the number of protons remains unchanged. Atomic number also gives number of electrons. Electrons are present in shells which participate in chemical reactions and decide chemical properties. Whereas relative atomic mass is the sum of the number of protons and number of neutrons so the number is more important in predicting the chemical properties of elements.

 22. What are the advantages of the Periodic Table?

Ans: In periodic table elements are arranged in a tabular form. So it is easy to remember the properties of elements if the position is known. Also the compounds formed by the elements are predictable if the position of the element is known. Periodic table made it easy and systematic to study chemistry.

 23. Which of the following electronic configuration are wrong and why?

 2,8,2

Ans: From the given electronic configuration, 2,8,9,1 is wrong because in the third shell the maximum number of electrons is 8. The correct electronic configuration is 2,8,8,2.

24. What are ions? What are its two types?

Ans: When one or more electrons are detached from a neutral atom, a positively charged particle is formed and called an ion. Ions may be cations and anions.

25. Show diagrammatically the formation of ${{O}^{2-}}$ ion?

Ans: Atomic number of oxygen is 8 and its electronic configuration is 2,6. In the outermost shell oxygen has 6 electrons. To complete its octet and become stable it needs 2 electrons. By gaining 2 electrons it becomes ${{O}^{2-}}$ ion.

Diagrammatic representation of formation of ${{O}^{2-}}$ ion is as follows:

26. Define isotopes and isobars?

Ans : Isotopes are atoms which have identical atomic numbers but different mass numbers. Examples of isotopes are ${}_{6}^{12}C,{}_{6}^{14}C$.

Isobars are atoms that have different atomic numbers but the same mass number. Examples of isobars are ${}_{18}^{40}Ar,{}_{19}^{40}K$.

Short Answer Questions (3 Marks)

27. For the symbol H, D and T tabulate three subatomic particles found in each of them.

Ans: H represents the hydrogen atom, D represents the deuterium atom and T represents the tritium atom. Three subatomic particles present in each of them is represented as follows:

28. Write the electronic configuration of any one pair of isotopes and isobars.

Ans: Electronic configuration of pairs of isotopes of carbon is ${}_{6}^{12}C,{}_{6}^{14}C$. Isotopes have the same number of electrons and protons.

Electronic configuration of a pair of isobars of argon and calcium is ${}_{18}^{40}Ar,{}_{20}^{40}Ca$.

29. Compare the properties of electrons, protons and neutrons.

Ans: Comparison of electrons, protons and neutrons is as follows:

30. What are the limitations of Rutherford’s model of the atom?

Ans: Rutherford’s model of atom is failed to explain the stability of atom because as per his model electrons revolve around the nucleus and while moving through orbit should emit energy and this energy loss will shrink the orbit and finally the electron would hit the nucleus and thus atom is unstable but it is not true.

31. Define valency by taking examples of silicon and oxygen.

Ans : The valency of electrons is determined by electrons present in the outermost shell of an atom. Electrons present in the outermost shell of an atom are known as the valence electrons. Electrons gain or lose electrons to complete its octet. The valency of silicon is 14 and electronic configuration is 2,8,4. So silicon can gain or lose 4 electrons. So the valency of silicon is +4 or -4.

Atomic number of oxygen is 8 and the electronic configuration is 2,6. To complete its octet oxygen gains 2 electrons hence the valency of oxygen is 2.

32. If bromine atom is available in the form of, say, two isotopes ${}_{35}^{79}Br(49.7%)$ and ${}_{35}^{81}Br(50.3%)$, Calculate the average atomic mass of bromine atom.

Ans: The average atomic mass of bromine is 

$=\dfrac{79\times 49.7+81\times 50.3}{100}$ 

$=\dfrac{3926.3+4074.3}{100}$ 

$=\dfrac{8000.6}{100}$ 

$=80u$ 

Average atomic mass of bromine atoms is 80 u.

33. The average atomic mass of a sample of an element X is 16.2 u. What are the percentages of isotopes ${}_{8}^{16}X$ ${}_{8}^{18}X$ and in the sample?

Ans: Average atomic mass of sample is given as

$\dfrac{16X+18\times \left( 100-X \right)}{100}$ 

 $\Rightarrow 16.2=\dfrac{16X+18\times \left( 100-X \right)}{100}$

$\Rightarrow 1620=-2X+1800$

$\Rightarrow 2X=1800-1620$

$\Rightarrow 2X=180$

$\therefore X=90$ 

The percentage of isotopes is ${}_{8}^{16}X(90%)$ and ${}_{8}^{18}X(10%)$.

34. In a gold – foil experiment:

Why did many $\alpha -$ particles pass through the gold foil undeflected?

Ans: Most of the space within the atom was empty so many $\alpha -$ particles passed through the gold foil undeflected.

Why did few $\alpha -$ particles deflect through small angles.

Ans: In a gold foil at center there is a positive charge so few $\alpha -$ particles deflect through small angles.

Why did few $\alpha -$ particles, after striking the gold foil, retrace their path.

Ans : In a gold foil there is a positively charged nucleus which is very tiny so few $\alpha -$ particles, after striking the gold foil, retrace their path.

 Compare the three major particles in atoms with respect to their mass and charge?

Ans: Comparison of three major particles proton, neutron and electron with respect to their mass and charge is as follows:

Inside an atom electron revolves around the nucleus in a circular path. Protons and neutrons are present inside the nucleus.

35. Write an experiment to show cathode rays are deflected by magnetic fields?

Ans: Experiment to show that cathode rays were deflected by magnetic fields is as follows:

First take a discharge tube with fluorescent material inside it.

Place a horse – shoe magnet in the center of the discharge tube.

When cathode rays are produced and travel through the discharge tube, then cathode rays get deflected by the magnetic field of the magnets in the direction of anode. Also they are negatively charged.

The diagram of experiment is as follows:

36. Write the postulates of Bohr theory?

Ans : The postulate of Bohr’s theory is as follows:

An electron revolves around the nucleus in the orbit of an atom in a definite path known as orbits or shells.

Energy of each orbit is fixed.

Energy increases from inner shell to the outer shells i.e. energy for orbit nearest the nucleus is lowest.

If energy is supplied then the electron moves from lower orbit to higher orbit.

37. Explain the variation of atomic radius along a period and down a group.

Ans: The atomic radius of an atom increases when we move down as an extra shell is added. The atomic radius decreases when we move from left to right as the nuclear charge of an element increases.

38. Why metals are electropositive and non-metals are electronegative in nature?

Ans : Metals are electropositive in nature because all metals give away electrons from their outermost shell in order to complete the octet and become stable. So metals become positively charged. Non-metals are electronegative in nature because all non-metals gain electrons in order to complete the octet and become stable. So non-metals become negatively charged.

39. Explain the formation of $A{{l}^{3+}}$ ion and why is it formed?

Ans: Aluminum has an atomic number of 13. The electronic configuration of Al is 2,8,3. It has 3 electrons in the outermost shell and to become stable it needs to complete its octet. In the outermost shell, the maximum number of electrons must be 8. So it is easy to lose 3 electrons and complete the octet. By giving away the 3 outermost electrons it becomes  $A{{l}^{3+}}$ ion.

40. Find the percentage composition of sucrose $\left( {{C}_{12}}{{H}_{22}}{{O}_{11}} \right)$.

Ans: The molecular mass of sucrose $\left( {{C}_{12}}{{H}_{22}}{{O}_{11}} \right)$ is

$\left( {{C}_{12}}{{H}_{22}}{{O}_{11}} \right)=12\times 12+22+11\times 16$

$\left( {{C}_{12}}{{H}_{22}}{{O}_{11}} \right)=144+22+176$

$\left( {{C}_{12}}{{H}_{22}}{{O}_{11}} \right)=342g/mol$

342 g of sucrose contains 144g Carbon, 22 g Hydrogen and 176 g Oxygen.

So 100 g sucrose contains:

$C=\dfrac{100\times 144}{342}=42.11g$ 

\[H=\dfrac{100\times 22}{342}=6.43g\]

$O=\dfrac{100\times 176}{342}=51.46g$

So the percentage composition of sucrose is

$C=42.11%$ 

$H=6.43%$ 

$O=51.46%$.

41. Complete the following table:

Ans: In the given table element is represented as ${}_{Z}^{A}X$.

Here, X is the symbol of element,

Z is the symbol of atomic number which is equal to number of protons,

A is the symbol of mass number which is equal to the sum of the number of protons and the number of neutrons.

By using above information we get the complete table as:

 Calculate the following:

 The number of gram – atoms of oxygen

Ans: Oxygen atoms are represented as ${{O}_{2}}$.  In oxygen 2 gram atoms are present.

 The number of atom of oxygen

Ans : Gram atomic mass of oxygen is $6.023\times {{10}^{23}}atoms$.

16 g of oxygen has $6.023\times {{10}^{23}}atoms$.

So 32 g of oxygen has $\dfrac{6.023\times {{10}^{23}}\times 32}{16}=1.205\times {{10}^{24}}atoms$. 

The number of molecules in 32 g of ozone $\left[ {{O}_{3}} \right]$.

Ans: We know that 48 g of ozone contains $6.023\times {{10}^{23}}molecules$.

So 1 g of ozone contains \[\dfrac{6.023\times {{10}^{23}}}{48}\] molecules.

Thus 32 g of ozone has \[\dfrac{6.023\times {{10}^{23}}\times 32}{48}=4.015\times {{10}^{23}}molecules.\]

 What mass of water will contain the same number of molecules as 8.0 g of ferrous oxide [FeO]?

Ans : We know that the atomic mass of 18 g of water is $6.023\times {{10}^{23}}atoms$.

Ferrous oxide is $56+16=72g$ 

So the atomic mass of 72 g of FeO is $6.023\times {{10}^{23}}atoms$.

Now, 1 g of FeO is \[=\dfrac{6.023\times {{10}^{23}}}{72}\] 

Also, 8 g of FeO is \[=\dfrac{6.023\times {{10}^{23}}\times 8}{72}\].

8 g of FeO is \[=0.669\times {{10}^{23}}\].

Now, 18 g of water is $6.023\times {{10}^{23}}atoms$.

$\dfrac{18}{6.023\times {{10}^{23}}}gms=1\text{ }atom$ 

$\Rightarrow \dfrac{18\times 0.669\times {{10}^{23}}}{6.023\times {{10}^{23}}}gms=0.669\times {{10}^{23}}\text{ }atoms$

Therefore, 2g of water contains \[=0.669\times {{10}^{23}}\].

So 2g of water will contain the same number of molecules as 8 g of ferrous oxide.

Long Answer Questions (5 Marks)

42. How will you find the valency of chlorine, Sulphur and magnesium?

Ans: The valency of electrons is determined by electrons present in the outermost shell of an atom. Electrons present in the outermost shell of an atom are known as the valence electrons. Those electrons determine the valency of that atom.

The atomic number of chlorine is 17 and the electronic configuration is 2,8,7.

Thus chlorine has 7 electrons in the outermost shell and to complete its octet it needs 1 more electron. So the valency of chlorine is one.

The atomic number of Sulphur is 16 and the electronic configuration is 2,8,6.

Thus Sulphur has 6 electrons in the outermost shell and to complete its octet it needs 2 more electrons. So the valency of Sulphur is two.

The atomic number of Magnesium is 12 and the electronic configuration is 2,8,2.

Thus Magnesium has 2 electrons in the outermost shell. It is easy to give away two valence electrons. So the valency of Magnesium is two.

43. Describe Bohr’s model of the atom.

Ans : There are some drawbacks in Rutherford’s atomic model. So to overcome this and to explain the structure of atoms in detail Neil Bohr in 1912 proposed a model of atoms. The postulates of Bohr’s model are given below:

An electron revolves around the nucleus in the orbit of an atom with fixed energy.

Energy of orbits increases from inner shell to the outer shells i.e. energy for orbit nearest the nucleus is lowest.

If energy is supplied then the electron moves from lower orbit to the higher orbit and if an electron jumps from higher orbit (energy level) to the lower orbit (energy level) then energy is emitted as electromagnetic waves.

Each orbit or shell represents an energy level by an integer number as n=1,2,3,….  Such orbits are characterized as K,L,M,N……….. and titled from nucleus side to outwards.

44. Compare all the proposed models of an atom given in this chapter.

Ans: There are three proposed models of an atom are discussed in detail i.e. Thomson’s model, Rutherford’s model and Bohr’s model.

The comparison between the three is given below:

45. Summarize the rules for writing of distribution of electrons in various shells for the first eighteen elements.

Ans: The following rules are followed for writing the number of electrons in different energy levels or shells:

The maximum number of electrons existing in a shell is given by the formula $2{{n}^{2}}$, where ‘n’ is the orbit number or energy level and is equal to 1,2,3,…

Hence the maximum number of electrons in different shells are as follows:

In the first orbit or also known as K-shell it will be $2\times {{1}^{2}}=2$ (n=1).

In the second orbit or also known as L-shell will be $2\times {{2}^{2}}=8$ (n=2).

In the third orbit or also known as M-shell will be $2\times {{3}^{2}}=18$ (n=3) and so on.

In the outermost shell the maximum number of electrons can be 8.

First inner shells are filled then outer shells are filled. Electrons are not put up in a given shell, unless the inner shells are filled. That

46. Explain following with examples and Give any two uses of isotopes.

Atomic number

Ans: Atomic number of an atom is equal to the number of protons present inside the nucleus of that atom. It is represented by Z.

Mass number

Ans: The atomic mass of an atom is the sum of masses of protons and neutrons present in its nucleus. It is represented by A. For example, the mass number of Carbon is 12 u because it has 6 protons and 6 neutrons in its nucleus.

Ans: Isotopes are atoms which have identical atomic numbers but different mass numbers. Examples of isotopes are ${}_{6}^{12}C,{}_{6}^{14}C$.

Ans : Isobars are atoms that have different atomic numbers but the same mass number. Examples of isobars are ${}_{18}^{40}Ar,{}_{19}^{40}K$. Total number of neutrons is the same in the atoms.

Two uses of isotopes are as follows:

An isotope of uranium is used in nuclear reactors as a fuel.

An isotope of cobalt is used in the treatment of cancer.

47. Complete the following table.

Ans: The complete table is as follows:

Chapter 4 Science Class 9 Important Questions

Chapter 4 structure of the atom is the part of atomic physics. Some of the scientists who have greatly contributed to modern atomic theory by finding actual evidence are John Dalton, J.J. Thompson, Ernest Rutherford, Niels Bohr, James Chadwick and Ernest Schrodinger.

Topics covered under the structure of atom Class 9 important questions are charged particles in matter, the structure of an atom, Thomson’s model of an atom, rutherford model of an atom, Bohr’s model of an atom, neutrons, distribution of electrons in different orbits, valency, atomic number,  mass number, isotopes and isobars. In this chapter, we also get to know about the discovery of electrons and protons  J.J. Thomson and E.Goldstein, respectively. From the mentioned topics many different questions can be framed in Class 9 Science Chapter 4 important questions.

Structure of Atom

It consists of three main particles: protons, electrons, and neutrons. The nucleus of the atom contains protons which are positively charged and neutrons with no charge.  The outermost region of the atoms is called an electron shell and contains an electron, which is a negatively charged particle.

Key Benefits of CBSE Class 9 Science Chapter 4 Important Questions

Here are some of the benefits of referring to Class 9 Science Chapter 4 Important Questions:

Awareness of Key Topics: Practising important questions provides a clear understanding of the crucial topics covered in the chapter.

Skill Development: Solving these questions enhances time management and problem-solving skills across all vital topics.

Understanding Question Formats: Students gain insights into the difficulty levels and various question formats that may appear in exams.

Confidence Boost: Repeated practice instills confidence in students, making them more assured in tackling exam questions.

Versatility in Exam Preparation: Students become well-prepared to handle any type of questions that may arise in the exam.

Students can find the important question of structure of atom Class 9 on Vedantu, which has been prepared by experts to help students with their annual exam preparation. The correct solution to the important questions is given in the PDF. By this, students can save a lot of time in finding the correct answer for the respective question. To know more about this chapter, download the solution of Class 9 Chapter 4 from our site. Chapter 4 has a good weightage in the final exam. By revising the concepts of Chapter 4, you can achieve almost 10 marks from this chapter.

Important Related Links for CBSE Class 9 

FAQs on Important Questions for CBSE Class 9 Science Chapter 4 - Structure of the Atom

1. What is the structure of an atom according to Chapter 4 of Class 9 Science?

We learned in Chapter 4 of Class 9 Science that an atom is made up of a nucleus surrounded by electrons and a nucleus made up of protons and neutrons. Electrons have a negative charge, while protons have a positive charge, and neutrons have no charge. The electrons are thought to travel in circular orbits of specified radii corresponding to discrete energy states with the nucleus at the centre in a simplified description of the atomic structure based on the Bohr model. The atom may thus be thought of as being made up of circular shells of electrons, with the lowest shell corresponding to the lowest energy state and the higher level shells having more energy.

2. Why are NCERT Solutions of Chapter 4 of Class 9 Science important?

The NCERT Solutions are a must before every examination and they cumulatively cover all the important concepts. All the NCERT based questions follow a certain pattern and they are extremely essential as this pattern is also adhered to in the examination. Make sure you practice all the NCERT Solutions numerous times to get a good understanding of the concept and further, to leave no scope for error in your exams.

3. What is inside the atom according to Chapter 4 of Class 9 Science notes?

There are a couple of components inside an atom according to Chapter 4 of Class 9 Science. Atoms are the fundamental components of matter. The proton, neutron, and electron are the three subatomic particles that make up the smallest unit of matter. Protons, neutrons, and electrons make up the basic structure of an atom. The mass and charge of the atoms are provided by these fundamental components. The proton and neutron make up the nucleus, with the electron circling around it. Students can learn more about this topic from Vedantu and the study material is absolutely free of cost.

4. What is Z in chemistry according to Chapter 4 of Class 9 Science?

The number of protons in the nucleus of every atom of a chemical element is known as the atomic number or proton number which has the symbol Z. A chemical element's atomic number is the only way to identify it and it makes an element unique. It is the same as the nucleus' charge number. The atomic number is also equivalent to the number of electrons in an uncharged atom.

5. What are neutrons in accordance with Chapter 4 of Class 9 Science?

Chadwick found another subatomic particle with a mass almost equal to that of a proton but no charge. It was given the name neutron later on. Except for hydrogen, all atoms have neutrons in their nuclei. In general, a neutron is denoted by the letter ‘n’. The total of the masses of the protons and neutrons in the nucleus determines the mass of an atom. Neutrons are introduced in the Chapter 4 of Class 9 Science and they are explained thoroughly in the NCERT notes.

CBSE Class 9 Science Important Questions

Cbse study materials.

NCERT Solutions for Class 9 Science Chapter 4 Structure of the Atom

Chapter 4 Structure of Atom NCERT Solutions for Class 9 Science

Contact form.

Extra Questions for Class 9 Science Chapter 4 Structure of the Atom

Extra questions for Class 9 Science Chapter 4 Structure of the Atom with answers is given below. Our subject expert prepared these solutions as per the latest NCERT textbook. These questions will be helpful to revise the all topics and concepts. CBSE Class 9 extra questions are the most simple and conceptual questions that are prepared by subject experts for the students to study well for the final exams. By solving these extra questions, students can be very efficient in their exam preparations.

Structure of the Atom Class 9 Science Extra Questions and Answers

Very short answer questions.

1: Draw the atomic structure of hydrogen atom. Answer:

2: Why are some elements chemically inert? Answer:  Because their outermost shell is completely filled.

3: Why is atom electrically neutral? Answer:  It has same number of protons and electrons, (positive charge = negative charge).

4: What is the charge and mass of a-particles? Answer:  Charge is + 2 Mass is 4 a.m.u.

5: What are valence electrons? Answer:  Electrons present in the outermost shell of an atom are called valence electrons.

6: An atom has atomic number 12, what is its valency and name the element? Answer:  Atomic number = 12 ∴ Protons = Electrons = 12 Electrons Configuration = K L M -2 8 2 ∴ Valency = 2 Element is magnesium.

7: Find the number of neutrons in  27 13 X. Answer:  Mass number = 27 ∴ p + n = 27 p = 13, (Atomic No. = Number of protons) ∴ 13 + n = 27 ∴ n = 14 ∴ Neutron =14

8: Where is the mass of atom is concentrated? Answer:  Mass of an atom is concentrated in nucleus.

9: Name two elements with same number of protons and neutrons? Answer:  Carbon (Protons = Neutrons = 6) Oxygen (Protons = Neutrons = 8)

10: Draw the atomic structure of sodium atom. Answer: 

11: Name the isotope used for treatment of cancer. Answer:  Isotope of cobalt. 12: AZX What does this symbol represent? Answer:  X → Symbol of element A → Mass number Z → Atomic number

13: Can the value of ‘Z’ be same for two different atoms? Answer:  No, (Z = atomic number), two different atoms cannot have same atomic number.

14: Can the value of A’ be same for two different atom? Answer:  Yes, it can be e.g. Ca and Ar has A-40 (i.e., mass number).

Short Answer Type Questions

1: Name the scientist who discovered protons and neutrons in an atoms. Answer:  Protons were discovered by E. Goldstein in 1866 and neutrons were discovered by J, Chadwick in 1932.

2: What is the contribution of Bohr and Bury together in the structure of atom’s explanation? Answer:  Both Bohr and Bury gave the distribution of electrons into different atoms by giving the formula 2n 2 , where n = shell number.

3: Draw the atomic structure of (i) an atom with same number of sub-atomic particles, (ii) an atom with same number of electrons in L and M shell.

Answer:  (i) An atom with same number of sub-atomic particles is He No. of protons = 2 No. of electrons = 2 No. of neutrons = 2

(ii) An atom with L and M shell filled → K L M- 2 8 8

4: What is an octate? Why would atoms want to complete their octate?

Answer:  When the outermost shell of an atom i.e., L, M or N are completely filled with 8 electrons in the shell, it is said an octate. Atoms would want to complete their octate because they want to become stable. 

5: Find the valency of  14 7 N and  35 17 Cl.

Answer:  The atomic number of nitrogen = 7, No. of protons = 7, No. of electrons = 7 Electronic configuration = K L M = 2 5 – Valency = 3 Because either it will gain three electrons or share 3 electrons to complete its octate. The atomic number of chlorine = 17, p = 17, e=17 Electronic configuration = K L M= 2 8 7 Valency = 1 Because it will gain 1 electron to complete its octate. 

8: What are nucleons? What is the name given to those atoms which have same number of nucleons in it?

Answer:  Protons and neutrons present in the nucleus are called nucleons Isobaric elements have same number of nucleons in it.

9: Give the difference between three sub-atomic particles.

Answer:  Three sub-atomic particles are electron, proton and neutron

10. Give the names of three atomic species of hydrogen. Answer:  Three atomic species of hydrogen are:

11: Atomic Mass exists as whole number, why do we write the atomic mass of chlorine as 35.5 u.

Answer:  Chlorine has two isotopes and the mass of an atom is taken as the average mass of all the naturally occurring atoms of that element. This is obtained by knowing the percentage of each isotopic from and then the average mass is calculated Cl = 35 – 75% and Cl = 37 – 25% = 35.5 u

12:  Give difference between isotopes, and isobars. Answer:

13: Number of protons and electrons are same in an atom. Then why is it wrong to say that atomic number of an atom is equal to its number of electrons.

Answer:  Atomic number ≠ Number of electrons, although number of protons = number of electrons because the electron’s number can change in an atom by loss, or gain of it. But the proton’s number remain constant (as it does not take part in loss or gain). 14: An atom is electrically neutral, on loss or gain of electrons why does it become charged?

Answer:  An atom is electrically neutral because of same number of protons and electrons. But it becomes charged, to become stable atom, loses or gains electrons. Hence, Number of protons ≠ Number of electrons If it loses electrons p > e; hence +ve charge is obtained. If it gains electrons e > p; hence -ve charge is obtained. 15: What is valency? Explain different types of valencies. Answer:  The combining capacity of an atom is called its valency. There are 2 types of valencies.

Some atoms also show zero valency when there outermost shell is completely filled. 16:  With the help of an activity in daily life, how can you prove that atoms are divisible. 

Answer:   Activity

• Take a scale, rub it on hair, try to attract a small bit of paper.
• Now divide the bit of paper further into smaller pieces
• Again bring the charged scale near to this pieces of papers.
• You will observe that the bits of paper still get attracted.

Conclusion:  This activity shows that atom contains charges and these charges are opposite in nature which shows the attraction. Hence here scale and paper both are oppositely charged and hence attract each other. Also, every atom has at least one sub-atomic particle.

17: In the structure of an atom why are protons present in the centre and are not pulled outside by the electrons as both are oppositely charged with same unit of charge?

Answer:  Protons are heavy with mass 1 unit and hence are concentrated in the centre   of the atom. The mass of electrons is negligible i.e.1/1800 times less than that of protons. Hence are not able to attract the protons and pull them out of the nucleus, although their charge is of same value. 

18: According to you, among the structure of atom studied which model is correct and why?

Answer:  Bohr’s model of an atom is the best model and is correct because it gives the explanation of nucleons (protons and neutrons) in the centre and how electrons revolve around the nucleons in their discrete, special orbits, so electrons don’t loose/radiate energy and remain bonded in their shell. 

Long Answer Type Questions

1. Give an activity to understand the implications of Rutherford’s a scattering experiment by a gold foil.

Answer:  To understand the implications of Rutherford’s a-particle scattering experiment: Activity:  Let a child stand in front of a wall with his eyes closed. Let him throw stones at the wall from a distance. He will hear sound for each strike of stone on the wall. This is like a nucleus of the atom. But if a blind-folded child has to throw stones at a barbed-wire fence, most of the stones would not hit the fencing and no sound would be heard. This is because there are lots of gap in the fence which allows the stone to pass through them. This is like empty space in an atom through which a-particles will pass through. Based on the above activity and similar reasoning Rutherford concluded the a-particle scattering experiment as: (1) Most of the space inside the atom is empty as a-particles passed through the foil. (2) Very few particles deflected from their path, this show that positive charge occupies less space. (3) A very small fraction of a-particles are deflected by 180°, this shows that all the positive charge and mass of the gold atom were concentrated in a very small volume within the atom.

2: What are isotopes? State its characteristics, give uses of isotopes?

Answer:  Atoms of same element with same atomic number but different mass number are isotopes. Characteristics:  (1) Physical properties of the isotopes are different e.g. mass, density. (2) Chemical properties of the isotopes are same due to same number of electrons. Uses: (1) Uranium isotope is used as a fuel in nuclear reactor (U-235). (2) Cobalt isotope is used for treatment of cancer (Co-60). (3) Iodine isotope is used in the treatment of goitre.

3: Explain Rutherford’s α-particle scattering experiment and give its observation and conclusion drawn.

Answer:   Rutherford’s α-particle scattering experiment: Fast moving α-particles were made to fall on a thin gold foil. Particles have + 2 charge and 4u mass, and considerable amount of energy.

Observations: (1) Most of the α-particles passed straight through the foil. (2) Some of the α-particles were deflected by small angles by the foil. (3) One out of every 12000 particles rebounded.

Conclusion from observation: (1) Most of the space inside the foil is empty. (2) Positive charge of atom occupies very less space. (3) Mass of the atom is concentrated in the centre with all positive charge concentrated in small volume within the atom.

4: Establish the relationship between atomic number, mass number, isotopes, isobars and valency of an atom.

Answer:  Atomic number — Gives the number of protons (Z) Mass number — Gives the number of protons and neutrons (A) Isotopes — When atoms of same element have same number of protons (Z) but different number of a neutrons (s) such atoms are called isotopes. Isobars — When atom of different element have same mass number (A) but different atomic number (Z) such atoms are called isobars. Valency — It is the combining capacity of an atom.

Value Based Questions

1: Aryan could not solve the following question in the group; his group mate explained him and solved his difficulty. The question was as follows: What information do you get from the given figure about the atomic number, mass number and valency of the given atom X’. (a) What is the answer for-the above question? (b) Name the element X’. (c) What value of Aryan’s friend is reflected in this behaviour?

Answer:  (a) The atomic number is 5. The mass number is 11. The valency is 3. (b) The element X’ is boron. (c) Aryan’s friend showed the value of helping and caring nature.

• Book Solutions
• State Boards

Case Study Questions Class 9 Science Matter in our Surroundings

Case study questions class 9 science chapter 1 matter in our surroundings.

CBSE Class 9 Case Study Questions Science Matter in our Surroundings. Important Case Study Questions for Class 9 Exam. Here we have arranged some Important Case Base Questions for students who are searching for Paragraph Based Questions Matter in our Surroundings.

At Case Study Questions there will given a Paragraph. In where some Questions will made on that respective Case Based Study. There will various types of marks will given 1 marks, 2 marks, 3 marks or 4 marks.

CBSE Case Study Questions Class 9 Science – Matter in our Surroundings

Case study 1:.

1.) A matter is anything that has mass and occupies space. Pen, paper, clips, sand, air, ice, etc. are different forms of matter. Every matter is made up of small particles. These particles are so tiny that they can’t be seen with naked eyes. Let’s see about the different characteristics of particles of matter.

• All matter is made up of very small particles.
• .Particles of matter has spaces between them.
• Particles of matter are continuously moving.
• Particles of matter attract each other.

Answer the following questions by referring above paragraph.

i.) Which of following is not matter?

c.) smell of perfume

d.) None of these

ii.) Thoughts coming in our mind are example of matter. True or false

c.) None of these

iii.) Which of the following is true about particles of matter?

a.) Particles of matter has spaces between them

b.) Particles of matter are continuously moving

c.) Particles of matter attract each other

d.) All of these

iv.) Give 5 examples of matter in our surroundings

v.) Enlist all properties of particles of matter

Answer key-1

iv.) pen, pencil, notebook, ice and water

v.) Different characteristics of particles of matter are

Case Study 2:

2.) There are three states of matter – solid, liquid and gas.

Solids have a definite shape, distinct boundaries and fixed volumes, that is, have negligible compressibility. Solids have a tendency to maintain their shape when subjected to outside force. Solids may break under force but it is difficult to change their shape, so they are rigid.

Liquids have no fixed shape but have a fixed volume. They take up the shape of the container in which they are kept. Liquids flow and change shape, so they are not rigid but can be called fluid.

Gas as has indefinite shape, no fixed volume. Gas gets the shape and volume of container.

Gas has very low density hence are light. Gas can flow easily and hence are called fluid.

i.) Which of the following state of matter takes shape of container in which it is filled?

d.) Both b and c

ii.) Distance between particles of matter least in

iii.) Compressibility is least in case of

iv.) Give properties of solids.

v.) Give properties of Gases.

Answer key-2

iv.) properties of solid are given below

• Solid has fixed volume.
• Solid has fixed shape.
• Solid has high density.
• Solids are heavy.
• Solid does not flow.

v.) Properties of gases are

• Gas has indefinite shape
• Gas has no fixed volume.
• Gas gets the shape and volume of container.
• Gas fills the container completely.
• Gas has very low density.
• Because of low density gas are light.
• Gas can flow easily and hence are called fluid.

Case Study 3:

3.) What happens inside the matter during change of state? On increasing the temperature of solids, the kinetic energy of the particles increases. Due to the increase in kinetic energy, the

Particles start vibrating with greater speed. The energy supplied by heat overcomes the forces of attraction between the particles. The particles leave their fixed positions and start moving more freely. A stage is reached when the solid melts and is converted to a liquid. The minimum temperature at which a solid melts to become a liquid at the atmospheric pressure is called its melting point.

The temperature of the system does not change after the melting point is reached, till all the ice melts. This happens even though we continue to heat the beaker, that is, we continue to supply heat. This heat gets used up in changing the state by overcoming the forces of attraction between the particles. The amount of heat energy that is required to change 1 kg of a solid into liquid at atmospheric pressure at its melting point is known as the latent heat of fusion. So, particles in water at 0 0 C (273 K) have more energy as compared to particles in ice at the same temperature.

The temperature at which a liquid starts boiling at the atmospheric pressure is known as its boiling point. Boiling is a bulk phenomenon. Particles from the bulk of the liquid gain enough energy to change into the vapour state. A change of state directly from solid to gas without changing into liquid state is called sublimation and the direct change of gas to solid without changing into liquid is called deposition.

i.) A change of state directly from solid to gas without changing into liquid state is called

a.) Sublimation

b.) Deposition

c.) Boiling point

ii.) The direct change of gas to solid without changing into liquid is called

iii.) The energy supplied by heat to solid is used to overcome the forces of attraction between the particles. True or false

iv.) Define melting point and boiling point

v.) Define latent heat of fusion

Answer key-3

iv.) The minimum temperature at which a solid melts to become a liquid at the atmospheric pressure is called its melting point.

The temperature at which a liquid starts boiling at the atmospheric pressure is known as its boiling point.

v.) The amount of heat energy that is required to change 1 kg of a solid into liquid at atmospheric pressure at its melting point is known as the latent heat of fusion.

Case Study 4:

4 .) Do we always need to heat or change pressure for changing the state of matter? Can you quote some examples from everyday life where change of state from liquid to vapour takes place without the liquid reaching the boiling point? In the case of liquids, a small fraction of particles at the surface, having higher kinetic energy, is able to break away from the forces of attraction of other particles and gets converted into vapour. This phenomenon of change of a liquid into vapors at any temperature below its boiling point is called evaporation.

i.) Evaporation of liquid takes place at

a.) Boiling point

b.) Above boiling point

c.) Below boiling point

ii.) Evaporation takes place at surface of liquid because

a.) They are heavy as compare to other particles

b.) They have sufficient kinetic energy to break the force

c.) They are light weight as compare to other particles

iii.) During evaporation particles of liquid change into vapour

a.) From the surface

b.) From the bottom

c.) From all over the liquid

iv.) Define evaporation.

v.) Explain process of evaporation

Answer key-4

iv.) The phenomenon of change of a liquid into vapors at any temperature below its boiling point is called evaporation.

v.) In the case of liquids, a small fraction of particles at the surface, having higher kinetic energy, is able to break away from the forces of attraction of other particles and gets converted into vapour. This phenomenon of change of a liquid into vapors at any temperature below its boiling point is called evaporation.

Case Study 5:

5.) You must have observed that the rate of evaporation increases with–

• an increase of surface area:
• We know that evaporation is a surface phenomenon. If the surface area is increased, the rate of evaporation increases. For example, while putting clothes for drying up we spread them out.
• an increase of temperature:

With the increase of temperature, more number of particles get enough kinetic energy to go into the vapour state.

In an open vessel, the liquid keeps on evaporating. The particles of liquid absorb energy from the surrounding to regain the energy lost during evaporation. This absorption of energy from the surroundings makes the surroundings cold. What happens when you pour some acetone (nail polish remover) on your palm? The particles gain energy from your palm or surroundings and evaporate causing the palm to feel cool. After a hot sunny day, people sprinkle water on the roof or open ground because the large latent heat of vaporization of water helps to cool the hot surface.

i.) Evaporation is surface phenomenon. True or false

ii.) As temperature increases the rate of evaporation is

a.) increases

b.) decreases

c.) remains constant

iii.) The rate of evaporation increases with

a.) Increase in wind speed

b.) Decrease in wind speed

c.) Does not have any effect from wind speed

iv.) What happens when you pour some acetone (nail polish remover) on your palm?

v.) We are able to sip hot tea from saucer than from cup. Why?

Answer key-5

iv.) The particles gain energy from your palm or surroundings and evaporate causing the palm to feel cool.

v.) We are able to sip hot tea from saucer than from cup. This is because saucer has large surface area, due to large surface area as compare to cut area tea evaporates at faster rate.

Thank you It helped me a lot

Why smell of Perfume is not a matter?

Because there is no particle

Because their are perfume particles suspended in air

These all case study questions are really helpful . Thanks

This is my first I was so nervous but these questions help me alot thank you

Smell of perfume is a matter because it have gas particles means perfume particles

Leave a Reply Cancel reply

Your email address will not be published. Required fields are marked *

Save my name, email, and website in this browser for the next time I comment.

We have a strong team of experienced Teachers who are here to solve all your exam preparation doubts

Dav class 6 sst solution chapter 1 the planet earth and the solar system, dav class 6 sst solution chapter 5 the realms of the earth, dav class 6 sst solution chapter 22 democracy and government, sikkim scert class 5 english chapter 6b the smile of the terek sandpiper solution.

Sign in to your account

Username or Email Address

Remember Me

Gurukul of Excellence

Classes for Physics, Chemistry and Mathematics by IITians

Join our Telegram Channel for Free PDF Download

Case Study and Passage Based Questions for Class 9 Science Chapter 9 Force and Laws of Motion

• Last modified on: 2 years ago
• Reading Time: 6 Minutes

Case Study/Passage Based Questions:

Question 1:

Read the following and answer any four questions from (i) to (v) given below :

In the figure below the card is flicked with a push. It was observed that the card moves ahead while coin falls in glass.

(i) Give reason for the above observation. (a) The coin possesses inertia of rest, it resists the change and hence falls in the glass. (b) The coin possesses inertia of motion; it resists the change and hence falls in the glass. (c) The coin possesses inertia of rest, it accepts the change and hence falls in the glass. (d) The coin possesses inertia of rest, it accepts the change and hence falls in the glass.

(ii) Name the law involved in this case. (a) Newton’s second law of motion. (b) Newton’s first law of motion. (c) Newton’s third law of motion. (d) Law of conservation of energy

(iii) If the above coin is replaced by a heavy five-rupee coin, what will be your observation. Give reason. (a) Heavy coin will possess more inertia so it will not fall in tumbler. (b) Heavy coin will possess less inertia so it will fall in tumbler. (c) Heavy coin will possess more inertia so it will fall in tumbler. (d) Heavy coin will possess less inertia so it will not fall in tumbler.

(iv) Name the law which provides the definition of force. (a) Law of conservation of mass (b) Newton’s third law. (c) Newton’s first law (d) Newton’s second law.

(v) State Newton’s first law of motion. (a) Energy can neither be created nor be destroyed, it can be converted from one form to another, total amount of energy always remains constant. (b) A body at rest remains at rest or, if in motion, remains in motion at constant velocity unless it is acted upon by an external unbalanced force. (c) For every action in nature there is an equal and opposite reaction. (d) The acceleration in an object is directly related to the net force and inversely related to its mass.

Other Chapters:

Case Study and Passage Based Questions for Class 9 Science Chapter 3 Atoms and Molecules

Last modified on:2 years agoReading Time:5MinutesCase Study Questions for Class 9 Science Chapter 3 Atoms and Molecules In CBSE Class 9 Science Paper, Students will have to answer some questions based on Assertion and Reason. There will be a few questions based on case studies and passage based as well. In that, a paragraph will be given, and then…

Case Study and Passage Based Questions for Class 9 Science Chapter 4 Structure of Atom

Last modified on:2 years agoReading Time:4MinutesCase Study Questions for Class 9 Science Chapter 4 Structure of Atom In CBSE Class 9 Science Paper, Students will have to answer some questions based on Assertion and Reason. There will be a few questions based on case studies and passage based as well. In that, a paragraph will be given, and then…

Case Study and Passage Based Questions for Class 9 Science Chapter 10 Gravitation

Last modified on:2 years agoReading Time:4MinutesCase Study Questions for Class 9 Science Chapter 10 Gravitation In CBSE Class 9 Science Paper, Students will have to answer some questions based on Assertion and Reason. There will be a few questions based on case studies and passage based as well. In that, a paragraph will be given, and then questions based…

Case Study and Passage Based Questions for Class 9 Science Chapter 11 Work and Energy

Last modified on:2 years agoReading Time:4MinutesCase Study Questions for Class 9 Science Chapter 11 Work and Energy In CBSE Class 9 Science Paper, Students will have to answer some questions based on Assertion and Reason. There will be a few questions based on case studies and passage based as well. In that, a paragraph will be given, and then…

Case Study and Passage Based Questions for Class 9 Science Chapter 13 Why Do We Fall Ill

Last modified on:2 years agoReading Time:4MinutesCase Study Questions for Class 9 Science Chapter 13 Why Do We Fall Ill In CBSE Class 9 Science Paper, Students will have to answer some questions based on Assertion and Reason. There will be a few questions based on case studies and passage based as well. In that, a paragraph will be given,…

Download CBSE Books

Exam Special Series:

• Sample Question Paper for CBSE Class 10 Science (for 2024)
• Sample Question Paper for CBSE Class 10 Maths (for 2024)
• CBSE Most Repeated Questions for Class 10 Science Board Exams
• CBSE Important Diagram Based Questions Class 10 Physics Board Exams
• CBSE Important Numericals Class 10 Physics Board Exams
• CBSE Practical Based Questions for Class 10 Science Board Exams
• CBSE Important “Differentiate Between” Based Questions Class 10 Social Science
• Sample Question Papers for CBSE Class 12 Physics (for 2024)
• Sample Question Papers for CBSE Class 12 Chemistry (for 2024)
• Sample Question Papers for CBSE Class 12 Maths (for 2024)
• Sample Question Papers for CBSE Class 12 Biology (for 2024)
• CBSE Important Diagrams & Graphs Asked in Board Exams Class 12 Physics
• Master Organic Conversions CBSE Class 12 Chemistry Board Exams
• CBSE Important Numericals Class 12 Physics Board Exams
• CBSE Important Definitions Class 12 Physics Board Exams
• CBSE Important Laws & Principles Class 12 Physics Board Exams
• 10 Years CBSE Class 12 Chemistry Previous Year-Wise Solved Papers (2023-2024)
• 10 Years CBSE Class 12 Physics Previous Year-Wise Solved Papers (2023-2024)
• 10 Years CBSE Class 12 Maths Previous Year-Wise Solved Papers (2023-2024)
• 10 Years CBSE Class 12 Biology Previous Year-Wise Solved Papers (2023-2024)
• ICSE Important Numericals Class 10 Physics BOARD Exams (215 Numericals)
• ICSE Important Figure Based Questions Class 10 Physics BOARD Exams (230 Questions)
• ICSE Mole Concept and Stoichiometry Numericals Class 10 Chemistry (65 Numericals)
• ICSE Reasoning Based Questions Class 10 Chemistry BOARD Exams (150 Qs)
• ICSE Important Functions and Locations Based Questions Class 10 Biology
• ICSE Reasoning Based Questions Class 10 Biology BOARD Exams (100 Qs)

✨ Join our Online JEE Test Series for 499/- Only (Web + App) for 1 Year

✨ Join our Online NEET Test Series for 499/- Only for 1 Year

Leave a Reply Cancel reply

Join our Online Test Series for CBSE, ICSE, JEE, NEET and Other Exams

Editable Study Materials for Your Institute - CBSE, ICSE, State Boards (Maharashtra & Karnataka), JEE, NEET, FOUNDATION, OLYMPIADS, PPTs

Discover more from Gurukul of Excellence

Subscribe now to keep reading and get access to the full archive.

Type your email…

Continue reading

• NCERT Exemplar
• Science Exemplar Class 9
• Structure Of The Atom

NCERT Exemplar Class 9 Science Solutions for Chapter 4 - Structure of the Atom

Ncert exemplar solutions class 9 science chapter 4 – free pdf download.

NCERT Exemplar Solutions for Class 9 Science Chapter 4 Structure of Atom help students to learn the concepts thoroughly discussed in CBSE Class 9 Structure of Atom. Referring to NCERT Exemplar aids in laying a strong foundation for students’ future studies. Topics involved here are the basics and are helpful throughout their life. The PDF format of solutions is free to download and can be used by students while answering the questions from the NCERT Exemplar textbook.

NCERT Exemplar Solutions Class 9 Science provide you with MCQs, Atomic Structure short answer questions and long answers that will help you analyse the possible types of questions that may appear in Class 9 CBSE examinations and competitive examinations.  Instead of searching for the best reference book, students can directly access the solutions from BYJU’S. The answers for each and every chapter are designed by the subject experts with utmost care to help students grasp the important concepts.

Download the PDF the of NCERT Exemplar for Class 9 Science Chapter 4 – Structure of the Atom

Access Answers to the NCERT Exemplar Class 9 Science Chapter 4 – Structure of the Atom

Multiple choice questions.

1. Which of the following correctly represent the electronic distribution in the Mg atom?

(a) 3, 8, 1

(b) 2, 8, 2

(c) 1, 8, 3

(d) 8, 2, 2

Answer is 2, 8, 2

Explanation :

Atomic number of Mg is 12 hence electronic distribution will be 1s 2 2s 2 2p 6 3s 2 .

2. Rutherford’s ‘alpha (α) particles scattering experiment’ resulted in to discovery of

(a) Electron

(c) Nucleus in the atom

(d) Atomic mass

Answer is (c) Nucleus in the atom

Explanation:

Rutherford’s ‘alpha (α) particles scattering experiment’ experiment concludes that alpha particles returned to their original path. This showed the presence of a nucleus in the centre.

3. The number of electrons in an element X is 15 and the number of neutrons is 16. Which of the following is the correct representation of the element?

a)  31 X 15

Answer is (a)  31 X 15

Number of protons in an element depicts atomic number. A number of protons and electrons are equal in an element. Hence atomic number is written in subscript whereas the mass number is written in the subscript before the symbol of the element.

4. Dalton’s atomic theory successfully explained

(i) Law of conservation of mass

(ii) Law of constant composition

(iii) Law of radioactivity

(iv) Law of multiple proportion

(a) (i), (ii) and (iii)

(b) (i), (iii) and (iv)

(c) (ii), (iii) and (iv)

(d) (i), (ii) and (iv)

Answer is (d) (i), (ii) and (iv)

Dalton’s theory explains Law of conservation of mass, Law of constant composition, Law of multiple proportions. But it never gives any details of Law of radioactivity.

5. Which of the following statements about Rutherford’s model of atom are correct?

(i) considered the nucleus as positively charged

(ii) established that the α–particles are four times as heavy as a hydrogen atom

(iii) can be compared to solar system

(iv) was in agreement with Thomson’s model

(a) (i) and (iii)

(b) (ii) and (iii)

(c) (i) and (iv)

(d) only (i)

Answer is (a) (i) and (iii)

Positively charged alpha particles were deflected by the nucleus. This shows the nucleus is positively charged. Rutherford also postulated that electrons are arranged in an atom around the nucleus like planets arranged around the sun.

6. Which of the following are true for an element?

(i) Atomic number = number of protons + number of electrons

(ii) Mass number = number of protons + number of neutrons

(iii) Atomic mass = number of protons = number of neutrons

(iv) Atomic number = number of protons = number of electrons

(a) (i) and (ii)

(b) (i) and (iii)

(c) (ii) and (iii)

(d) (ii) and (iv)

Answer is (d) (ii) and (iv)

Atomic number Z is the number of protons present in an electron which is also equal to a number of the electron in an atom. Since the mass of a neutron is negligible, a number of protons and electron is added to obtain a mass number of an element.

7. In the Thomson’s model of atom, which of the following statements are correct?

(i) the mass of the atom is assumed to be uniformly distributed over the atom

(ii) the positive charge is assumed to be uniformly distributed over the atom

(iii) the electrons are uniformly distributed in the positively charged sphere

(iv) the electrons attract each other to stabilise the atom

(d) (i), (iii) and (iv)

Answer is(a) (i), (ii) and (iii)

According to Thomson, the model of an atom is similar to a Christmas pudding.The electrons are studded like currants in a positively charged sphere like Christmas pudding and the mass of the atom was supposed to be uniformly distributed.

8. Rutherford’s α–particle scattering experiment showed that

(i) electrons have a negative charge

(ii) the mass and positive charge of the atom is concentrated in the nucleus

(iii) neutron exists in the nucleus

(iv) most of the space in the atom is empty Which of the above statements are correct?

(b) (ii) and (iv)

(d) (iii) and (iv

Answer is (b) (ii) and (iv)

An atom consists of a positively charged, dense and very small nucleus which have all the protons and neutrons. The positive charge is due to protons, as neutrons have no charge. Here the space is empty because alpha particles pass straight through the gold foil without any deflection.

Thomson explained that electron s have a negative charge. Existence of neutron was discovered by Chadwick.

9. The ion of an element has 3 positive charges. Mass number of the atom is 27 and the number of neutrons is 14. What is the number of electrons in the ion?

Answer is (b) 10

Mass number (A) of the atom = 27

Number of the neutron in the atom =14

Number of Electrons=Mass number-Number of neutrons=27-14

Number of electrons= 13

Since ions of the element have 3 positive charges number of the electron in the ion is 13-3 which equal 10.

Hence the answer is 10

10. Identify the Mg2+ ion from the Fig.4.1 where, n and p represent the number of neutrons and protons respectively.

Answer is d)

Number of protons in Mg atom = 2+ 8 + 2 = 12

Number of neutrons in Mg atom = 24 -12 = 12

Therefore, option (d) is the correct answer

11. In a sample of ethyl ethanoate (CH3COOC2H5) the two oxygen atoms have the same number of electrons but different number of neutrons. Which of the following is the correct reason for it?

(a) One of the oxygen atoms has gained electrons

(b) One of the oxygen atoms has gained two neutrons

(c) The two oxygen atoms are isotopes

(d) The two oxygen atoms are isobars.

Answer is(c) The two oxygen atoms are isotopes

Two Oxygen atoms in CH 3 COOC 2 H 5  can have a different number of neutrons only if the two O-atoms are isotopes. Isotopes of an element have the same number of protons (and electrons) but a different number of neutrons.

12. Elements with valency 1 are

(a) always metals

(b) always metalloids

(c) either metals or non-metals

(d) always non-metals

Answer is (c) either metals or non-metals.

If the element shows positive valency it is a metal and if the element shows negative valency it will be a non-metal.

13. The first model of an atom was given by

(a) N. Bohr

(b) E. Goldstein

(c) Rutherford

(d) J.J. Thomson

Answer is (d) J.J. Thomson

14. An atom with 3 protons and 4 neutrons will have a valency of

Answer is (c) 1

15. The electron distribution in an aluminium atom is

(a) 2, 8, 3

(c) 8, 2, 3

(d) 2, 3, 8

Answer is (a) 2, 8, 3

Atomic number of Aluminium is 13, the First shell can have a maximum of 2 electron and the second shell holds a maximum of 8 electrons. Hence option a is the right answer.

16. Which of the following in Fig. 4.2 do not represent Bohr’s model of an atom correctly?

(c) (ii) and (iv)

(d) (i) and (iv)

Answer is ii and iv

The first shell can have a maximum of 2 electron and the second shell can have a maximum of 8 electrons hence ii and iv do not represent Bohr’s model of an atom correctly.

17. Which of the following statement is always correct?

(a) An atom has equal number of electrons and protons.

(b) An atom has equal number of electrons and neutrons.

(c) An atom has equal number of protons and neutrons.

(d) An atom has equal number of electrons, protons and neutrons.

Answer is (a) An atom has equal number of electrons and protons.

An atom is electrically neutral because the number of protons is always equal to a number of electrons. Hence option a) is right.

18. Atomic models have been improved over the years. Arrange the following atomic models in the order of their chronological order

(i) Rutherford’s atomic model

(ii) Thomson’s atomic model

(iii) Bohr’s atomic model

(b) (ii), (iii) and (i)

(c) (ii), (i) and (iii)

(d) (iii), (ii) and (i)

Answer is (c) (ii), (i) and (iii)

Thomson’s atomic model was proposed in the year 1904

Rutherford’s atomic model was proposed in the year 1911

Bohr’s atomic model was proposed in the year 1913

Short Answer Questions

19. Is it possible for the atom of an element to have one electron, one proton and no neutron. If so, name the element.

Yes, Hydrogen is the element which is having only 1 proton and 1 electron and no neutron hence there is no repulsive force in the nucleus hence it is stable.

20. Write any two observations which support the fact that atoms are divisible

• Ionic compounds are formed because of the formation of ions that involves the transfer of electrons.
• The presence of isotopes for the same element is possible due to the difference in the number of neutrons.

21. Will 35Cl and 37Cl have different valencies? Justify your answer.

35Cl and 37Cl cannot have different valencies because they are the isotopes of the same element.

22. Why did Rutherford select a gold foil in his α–ray scattering experiment?

Rutherford used gold for his scattering experiment because gold is the most malleable metal and he wanted the thinnest layer as possible.

Therefore, Rutherford selected a Gold foil in his alpha scattering experiment.

23. Find out the valency of the atoms represented by the Fig. 4.3 (a) and (b).

Atom (a) has zero valencies as it has 8 electrons in its valence shell making the configuration stable.

Atom (b) has a valency of +1 as it has 7 electrons in its outermost shell. It can accept 1 electron to achieve octet configuration.

24. One electron is present in the outer most shell of the atom of an element X. What would be the nature and value of charge on the ion formed if this electron is removed from the outer most shell?

If an electron is removed from the outermost shell a cation will be formed and the charge of the element will be +1.

25. Write down the electron distribution of chlorine atom. How many electrons are there in the L shell? (Atomic number of chlorine is 17).

Atomic number of chlorine atom = 17

So, its electronic configuration is

L shell of chlorine contains 8 electrons.

26. In the atom of an element X, 6 electrons are present in the outermost shell. If it acquires noble gas configuration by accepting requisite number of electrons, then what would be the charge on the ion so formed?

In this atom, 6 electrons are already present in its outermost orbitals. In order to attain a noble gas configuration element has to accept two-electron hence its charge is -2.

27. What information do you get from the Fig. 4.4 about the atomic number, mass number and valency of atoms X, Y and Z? Give your answer in a tabular form.

Atomic number, mass number and valency of atoms X, Y and Z

28. In response to a question, a student stated that in an atom, the number of protons is greater than the number of neutrons, which in turn is greater than the number of electrons. Do you agree with the statement? Justify your answer.

The statement is wrong because the number of protons can never be greater than the number of neutrons. The number of protons will always be less than or equal to the number of neutrons. The number of electrons and protons are always equal in a neutral atom.

29. Calculate the number of neutrons present in the nucleus of an element X which is represented as  31 X 15

Mass number = No. of protons + No. of neutrons = 31

∴ Number of neutrons = 31– number of protons

30. Match the names of the Scientists given in column A with their contributions towards the understanding of the atomic structure as given in column B

(A) – (B)

(a) Ernest Rutherford – (i) Indivisibility of atoms

(b) J.J.Thomson – (ii) Stationary orbits

(c) Dalton – (iii) Concept of the nucleus

(d) Neils Bohr – (iv) Discovery of electrons

(e) James Chadwick -(v) Atomic number

(f) E. Goldstein – (vi) Neutron

(g) Mosley – (vii) Canal rays

(a) Ernest Rutherford – (iii) Concept of the nucleus

(b) J.J.Thomson – (iv) Discovery of electrons

(c) Dalton – (i) Indivisibility of atoms

(d) Neils Bohr – (ii) Stationary orbits

(e) James Chadwick – (vi) Neutron

(f) E. Goldstein – (vii) Canal rays

(g) Mosley – (v) Atomic number

31. The atomic number of calcium and argon are 20 and 18 respectively, but the mass number of both these elements is 40. What is the name given to such a pair of elements?

Elements with different atomic numbers but same mass numbers are known as isobars. Calcium and argon are isobars.

32. Complete Table 4.1 on the basis of information available in the symbols given below

(a) 35 17 Cl (b) 12 6 C (c) 81 35 Br

33. Helium atom has 2 electrons in its valence shell but its valency is not 2, Explain

Helium has 2 electrons in its outermost shell thereby completing duplet configuration. Hence it has no valence shell left empty making its valency 0.

34. Fill in the blanks in the following statements

(a) Rutherford’s α-particle scattering experiment led to the discovery of the ———

(b) Isotopes have same ———but different———.

(c) Neon and chlorine have atomic numbers 10 and 17, respectively. Their valencies will be———and———respectively.

(d) The electronic configuration of silicon is ———and that of sulphur is ———

Soln: a) Rutherford’s α-particle scattering experiment led to the discovery of the atomic nucleus b) Isotopes have same atomic number but different mass number c) Neon and chlorine have atomic numbers 10 and 17, respectively. Their valencies will be 0 and 1, respectively. d) The electronic configuration of silicon is 2.8.4 and that of sulphur is 2.8.6

35. An element X has a mass number 4 and atomic number 2. Write the valency of this element?

Mass number = 4

Atomic number = 2

X is Helium.

It has 0 valency and it will not react with any other atom because it has its outer shell filled.

Long Answer Questions

36. Why do Helium, Neon and Argon have a zero valency?

Helium has 2 electrons in its outermost orbit, thus filling shell 1 and forming duplet configuration in the valence shell. Neon has 8 electrons in their valence orbit hence completing duplet configuration. In the same way, Argon and Neon have 8 electrons in its outermost shelling completing octet configuration. As these elements have a maximum electron in their valence shell thus reach stable electron configuration and they will not take part in any sort of chemical reactions.

37. The ratio of the radii of hydrogen atom and its nucleus is ~ 105. Assuming the atom and the nucleus to be spherical,

(i) What will be the ratio of their sizes?

(ii) If atom is represented by planet earth ‘Re ’ = 6.4 ×106 m, estimate the size of the nucleus.

38. Enlist the conclusions drawn by Rutherford from his α-ray scattering experiment.

Rutherford drawn following conclusion from his α-ray scattering experiment.

• α-particles passed through the gold foil without any deflection concluding the empty space inside the atom.
• Deflection is observed in few particles which prove the positive charge of the atom occupies very little space.
• Deflection in A very small fraction of α-particles indicates that all the positive charge and mass of the gold atom were concentrated in a very small volume within the atom.

39. In what way is the Rutherford’s atomic model different from that of Thomson’s atomic model?

Rutherford proposed that electron revolves around the nucleus in well-differentiated orbits. The nucleus is the centre which is positively charged. Rutherford proposed that the nucleus is very small and nearly all the mass of an atom is centred in the nucleus.

Thompson proposed that electron are scattered positively charged spheres like a Christmas pudding and the mass of the atom was supposed to be uniformly distributed.

40. What were the drawbacks of Rutherford’s model of an atom?

Rutherford’s model could not explain the stability of the atom.

Revolving electrons would lose energy as they are the charged particles and due to acceleration, charged particles would radiate energy.

The orbit of the revolving electron will reduce in size, following a spiral path as shown in the figure and ultimately the electron should fall into the nucleus. In other words, the atom should collapse.

41. What are the postulates of Bohr’s model of an atom?

Postulates of Bohr’s model of an atom are

• Only certain special orbits known as discrete orbits of electrons are allowed inside the atom.
• While revolving in discrete orbits the electrons do not radiate energy. These orbits or shells are called energy levels. These orbits or shells are represented by the letters K, L, M, N,… or the numbers, n=1,2,3,4,….

42. Show diagrammatically the electron distributions in a sodium atom and a sodium ion and also give their atomic number.

Atomic number of sodium (Z) =11 Mass number of sodium (A) = 23

Number of protons in the nucleus = 11 Number of neutrons in the nucleus =23-11 = 12

Number of electrons = 11

Electronic configuration of Na-atom = 2, 8, 1(K,L,M)

Na+ ion is formed from sodium atom by loss of an electron (present in the outermost shell). Hence,

the electronic configuration is 2, 8(K, L). However, the number of protons and neutrons remains the same.

43. In the Gold foil experiment of Geiger and Marsden, that paved the way for Rutherford’s model of an atom, ~ 1.00% of the α-particles were found to deflect at angles > 50º. If one mole of α-particles were bombarded on the gold foil, compute the number of α-particles that would deflect at angles less than 500.

Total number of α particles used for bombardment = 1 mole

1 mole=6.022×10 23 particles

number of α particles deflected at angles greater than 50°(>50°)= 1%

Number of α particles deflected at angles greater than 50° = 100-1 = 99%

The actual number of α particles deflected at angles less than 50°= 99/100 × 6.022 × 10 23

=5.96 × 10 23

NCERT Exemplar for Chapter 4 Structure of the Atom

Before solving the questions related to the chapter Structure of the Atom, let us learn what an atom is. An atom is the smallest constituent unit of ordinary matter that has the properties of chemical elements. Important topics related to this chapter are as listed.

• Atomic Number
• Mass Number

Important Topics of the NCERT Exemplar for Chapter 4 Structure of the Atom

• Charged Particles in Matter
• The Structure of An atom (2a) Thomson’s Model of an Atom (2b) Rutherford’s Model of an Atom (2c) Bohr’s Model of Atom (2d) Neutrons
• How Are Electrons Distributed in Different Orbits (Shells)
• Atomic Number and Mass Number (5a) Atomic Number (5b) Mass Number
• Isotopes (6a) Isobars

BYJU’S has the country’s top teachers and subject experts as mentors. Their experience will help you immensely in understanding the concepts and keeping them memorised for a long time. For NCERT study materials and to know about our innovative teaching methodology, download BYJU’S – The Learning App.

Frequently Asked Questions on NCERT Exemplar Solutions for Class 9 Science Chapter 4

What are the types of questions present in chapter 4 of ncert exemplar solutions for class 9 science, list out the topics discussed in chapter 4 of ncert exemplar solutions for class 9 science., where can i get ncert exemplar solutions for class 9 science chapter 4 online, leave a comment cancel reply.

Your Mobile number and Email id will not be published. Required fields are marked *

Request OTP on Voice Call

Post My Comment

• Share Share

Register with BYJU'S & Download Free PDFs

Register with byju's & watch live videos.