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CBSE Worksheets for Class 9 Chemistry

CBSE Worksheets for Class 9 Chemistry: One of the best teaching strategies employed in most classrooms today is Worksheets. CBSE Class 9 Chemistry Worksheet for students has been used by teachers & students to develop logical, lingual, analytical, and problem-solving capabilities. So in order to help you with that, we at WorksheetsBuddy have come up with Kendriya Vidyalaya Class 9 Chemistry Worksheets for the students of Class 9. All our CBSE NCERT Class 9 Chemistry practice worksheets are designed for helping students to understand various topics, practice skills and improve their subject knowledge which in turn helps students to improve their academic performance. These chapter wise test papers for Class 9 Chemistry will be useful to test your conceptual understanding.

Board: Central Board of Secondary Education(www.cbse.nic.in) Subject: Class 9 Chemistry Number of Worksheets: 30

CBSE Class 9 Chemistry Worksheets PDF

All the CBSE Worksheets for Class 9 Chemistry provided in this page are provided for free which can be downloaded by students, teachers as well as by parents. We have covered all the Class 9 Chemistry important questions and answers in the worksheets which are included in CBSE NCERT Syllabus. Just click on the following link and download the CBSE Class 9 Chemistry Worksheet. CBSE Worksheets for Class 9 Chemistry can also use like assignments for Class 9 Chemistry students.

• CBSE Worksheets for Class 9 Chemistry The Matter In Our Surroundings Assignment
• CBSE Worksheets for Class 9 Chemistry Atoms and molecules Assignment
• CBSE Worksheets for Class 9 Chemistry Atoms and molecules Assignment 2
• CBSE Worksheets for Class 9 Chemistry Atoms and molecules Assignment 3
• CBSE Worksheets for Class 9 Chemistry Experiments Assignment
• CBSE Worksheets for Class 9 Chemistry Is Matter Around Us Pure Assignment 1
• CBSE Worksheets for Class 9 Chemistry Is Matter Around Us Pure Assignment 2
• CBSE Worksheets for Class 9 Chemistry Matter in Our Sorrounding Assignment 1
• CBSE Worksheets for Class 9 Chemistry Matter in Our Sorrounding Assignment 2
• CBSE Worksheets for Class 9 Chemistry Matter in Our Sorrounding Assignment 3
• CBSE Worksheets for Class 9 Chemistry Structure of Atom Assignment 1
• CBSE Worksheets for Class 9 Chemistry Structure of Atom Assignment 2
• CBSE Worksheets for Class 9 Chemistry Assignment 1
• CBSE Worksheets for Class 9 Chemistry Assignment 2
• CBSE Worksheets for Class 9 Chemistry Assignment 3
• CBSE Worksheets for Class 9 Chemistry Assignment 4
• CBSE Worksheets for Class 9 Chemistry Assignment 5
• CBSE Worksheets for Class 9 Chemistry Assignment 6
• CBSE Worksheets for Class 9 Chemistry Assignment 7
• CBSE Worksheets for Class 9 Chemistry Assignment 8
• CBSE Worksheets for Class 9 Chemistry Assignment 9
• CBSE Worksheets for Class 9 Chemistry Assignment 10
• CBSE Worksheets for Class 9 Chemistry Assignment 11
• CBSE Worksheets for Class 9 Chemistry Assignment 12
• CBSE Worksheets for Class 9 Chemistry Assignment 13
• CBSE Worksheets for Class 9 Chemistry Assignment 14
• CBSE Worksheets for Class 9 Chemistry Assignment 15
• CBSE Worksheets for Class 9 Chemistry Assignment 16
• CBSE Worksheets for Class 9 Chemistry Assignment 17
• CBSE Worksheets for Class 9 Chemistry Assignment 18

Advantages of CBSE Class 9 Chemistry Worksheets

• By practising NCERT CBSE Class 9 Chemistry Worksheet , students can improve their problem solving skills.
• Helps to develop the subject knowledge in a simple, fun and interactive way.
• No need for tuition or attend extra classes if students practise on worksheets daily.
• Working on CBSE worksheets are time-saving.
• Helps students to promote hands-on learning.
• One of the helpful resources used in classroom revision.
• CBSE Class 9 Chemistry Workbook Helps to improve subject-knowledge.
• CBSE Class 9 Chemistry Worksheets encourages classroom activities.

Worksheets of CBSE Class 9 Chemistry are devised by experts of WorksheetsBuddy experts who have great experience and expertise in teaching Maths. So practising these worksheets will promote students problem-solving skills and subject knowledge in an interactive method. Students can also download CBSE Class 9 Chemistry Chapter wise question bank pdf and access it anytime, anywhere for free. Browse further to download free CBSE Class 9 Chemistry Worksheets PDF .

Now that you are provided all the necessary information regarding CBSE Class 9 Chemistry Worksheet and we hope this detailed article is helpful. So Students who are preparing for the exams must need to have great solving skills. And in order to have these skills, one must practice enough of Class 9 Chemistry revision worksheets . And more importantly, students should need to follow through the worksheets after completing their syllabus.  Working on CBSE Class 9 Chemistry Worksheets will be a great help to secure good marks in the examination. So start working on Class 9 Chemistry Worksheets to secure good score.

CBSE Worksheets For Class 9

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Assignments For Class 9 Chemistry

Assignments for Class 9 Chemistry have been developed for Standard 9 students based on the latest syllabus and textbooks applicable in CBSE, NCERT and KVS schools. Parents and students can download the full collection of class assignments for class 9 Chemistry from our website as we have provided all topic wise assignments free in PDF format which can be downloaded easily. Students are recommended to do these assignments daily by taking printouts and going through the questions and answers for Grade 9 Chemistry. You should try to do these test assignments on a daily basis so that you are able to understand the concepts and details of each chapter in your Chemistry book and get good marks in class 9 exams.

Assignments for Class 9 Chemistry as per CBSE NCERT pattern

All students studying in Grade 9 Chemistry should download the assignments provided here and use them for their daily routine practice. This will help them to get better grades in Chemistry exam for standard 9. We have made sure that all topics given in your textbook for Chemistry which is suggested in Class 9 have been covered ad we have made assignments and test papers for all topics which your teacher has been teaching in your class. All chapter wise assignments have been made by our teachers after full research of each important topic in the textbooks so that you have enough questions and their solutions to help them practice so that they are able to get full practice and understanding of all important topics. Our teachers at https://www.assignmentsbag.com have made sure that all test papers have been designed as per CBSE, NCERT and KVS syllabus and examination pattern. These question banks have been recommended in various schools and have supported many students to practice and further enhance their scores in school and have also assisted them to appear in other school level tests and examinations. Its easy to take print of thee assignments as all are available in PDF format.

Some advantages of Free Assignments for Class 9 Chemistry

• Solving Assignments for Chemistry Class 9 helps to further enhance understanding of the topics given in your text book which will help you to get better marks
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• Parents will be able to take print out of the assignments and give to their child easily.

All free Printable practice assignments are in PDF single lick download format and have been prepared by Class 9 Chemistry teachers after full study of all topics which have been given in each chapter so that the students are able to take complete benefit from the worksheets. The Chapter wise question bank and revision assignments can be accessed free and anywhere. Go ahead and click on the links above to download free CBSE Class 9 Chemistry Assignments PDF.

You can download free assignments for class 9 Chemistry from https://www.assignmentsbag.com

You can get free PDF downloadable assignments for Grade 9 Chemistry from our website which has been developed by teachers after doing extensive research in each topic.

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Structure of the Atom Class 9 Notes CBSE Science Chapter 4 (Free PDF Download)

• Revision Notes
• Chapter 4 Structure Of The Atom

CBSE Class 9 Science Chapter 4 - Structure of The Atom Revision Notes - Free PDF Download

The smallest unit of any matter which retains all the chemical properties of an element is called an atom. Molecules are formed by combining atoms which then interconnect and form solids, liquids, or gases. From the structure of an atom of Class 9 notes, you will know that an atom has two regions, a nucleus that forms the centre of the atom and contains neutrons and protons, and there is an outer region of an atom which keeps the electron in its orbit around the nucleus. Neutrons have a negative charge equal to the positive charge of a proton.

Vedantu is a platform that provides free CBSE Solutions (NCERT) and other study materials for students. You can also download Class 9 Maths and Class 9 Science NCERT Solutions to help you to revise the complete syllabus and score more marks in your examinations.

Important Topics Covered under the Chapter

Following are the important topics that are covered in Class 9 Science Chapter 4 - Structure of the Atom:

Sub-Atomic Particles of an Atom and Their Discovery

Atomic Model by Thomson

Electronic Arrangement in an Atom 

Atomic Model by Rutherford

Bohr’s Model of Atom

Atomic Number

Mass number, download cbse class 9 science revision notes 2024-25 pdf.

Also, check CBSE Class 9 Science revision notes for All chapters:

Access Class 9 Science Chapter 4 – Structure of Atoms Notes in 30 Minutes

Summary of structure of atoms.

Atoms are the basic units of matter and the defining structure of elements.

It consists of three basic particles, i.e., protons, electrons, and neutrons, that build the structure of an atom.

Protons are positively charged particles and were founded by E. Goldstein.

Electrons are negatively charged particles and were founded by J.J. Thomson.

Neutrons have no charge and were founded by Chadwick.

The nucleus is in the centre of the atom and contains protons and neutrons.

The outer region of the atom which holds electrons in orbit around the nucleus is known as shell/energy level/orbits. 

These shells are further divided into subshells.

The electrons present in the outermost shell of an atom are known as the valence electrons.

The electronic configuration of an element is the representation of the arrangement of electrons distributed among the orbital shells and subshells. The valence electrons are the determining factor for the unique chemistry of the element.

The atomic number of an element is the same as the number of protons in the nucleus of its atom. As atoms are electrically neutral, an atom contains as many electrons as it has protons. The atomic number is denoted by Z. 

The mass number of an atom is equal to the number of nucleons in its nucleus. Nucleons are the collective term for protons and neutrons. The mass number is denoted by A.

In the notation of an atom, the atomic number is written as a subscript on the left of the element symbol and the mass number is written as a superscript on the left of the element symbol.

Isotopes can be defined as elements that possess the same number of protons and electrons, but a different number of neutrons.

For example, Protium, deuterium, and tritium are the isotopes of hydrogen. They each have one single proton Z=1 and a single electron but differ in the number of their neutrons. Hydrogen has no neutrons, deuterium has one, and tritium has two neutrons.

Isobar is an element that differs in chemical property but has the same physical property which means isobars are those elements that have a different atomic number but the same mass number. 

For example, Calcium and chlorine are isobars since both have a mass number of 40 but calcium has an atomic number of 20 and chlorine has an atomic number of 17.

Isotones are elements that have the same number of neutrons but different atomic numbers.

For example, Chlorine with atomic number 37 and potassium with atomic number 39 is isotones because both chlorine and potassium have the same number of neutrons i.e., 20.

Chapter 4 Science Class 9 Notes: Atomic Number and Mass Number

Chapter 4 Science Class 9 notes tell us that the total number of protons present in an element is called the atomic number while the mass number is both the number of protons plus the number of neutrons.

According to Class 9 Chapter 4 Science notes, an atomic number is the number of the chemical elements present in the periodic system so that the elements are organised in order of the increasing number of protons present in the nucleus. Also, the total number of protons that are equal to the electrons in a neutral atom is called the atomic number. For example, iron has 26 protons in its nucleus; hence, the atomic number of the matter is 26.  An equal number of electrons and protons are presented in a neutral atom.

According to Class 9th Science Chapter 4 notes, the total number of protons and neutrons is combined together and forms an element’s mass number. The contribution of the mass from the electron is disdained and then calculated as the mass number. Hence, the approximation of the mass is used to calculate the number of neutrons that an element has by subtracting the total number of protons from the mass number. Both neutrons and protons weigh about 1 atomic mass unit or amu. Isotopes of this same element will have the same number of atoms but a different mass.

Class 9 Science Chapter 4 Notes: Details of Isotopes

Notes of Chapter 4 Science Class 9 also give us a brief description of isotopes. It is the variant of a specific chemical element that differs in its number of neutrons and also in the number of nucleons. The isotopes have the same number of protons and a different number of neutrons. Thus, they have the same atomic number but a different mass number. All elements are a mixture of isotopes. Each of them is a pure substance. They have the same chemical properties but different physical properties. If there is an absence of isotope in an element, then its mass would be the same as the total number of neutrons and protons. Chapter 4 Science Class 9 notes also tell us that if there is a presence of isotope in any element, then the percentage of all the isotope forms should be known and then the average mass should be calculated.

Science Class 9 Chapter 4 Notes: Details of Isobars

The nuclides of various chemical elements are called isobars. They have the same number of nucleons which means that they have the same mass number. But they differ in atomic number. Alfred Walter Stewart suggested the name “isobars”. It has been derived from the Greek word isos which means “equal” and bars, which means “weight”.

Class 9 Science Notes Chapter 4: A Summary of The Structure of An Atom

An atom is made from the nucleus which is the centre of the atom and carries protons and neutrons and an outer region that holds the electron in its orbit around the nucleus. 

All electrons have a negative charge which is equal to the positive charge of a proton.

Neutrons are known as uncharged particles that are found in the nucleus.

Benefits of Studying Vedantu’s Revision Notes on CBSE Class 9 Science Chapter 4 - Structure of the Atom

The advantages of studying the CBSE Revision Notes on Class 9 Science Chapter 4 - Structure of the Atom, by Vedantu, are many. However, the following are the most noteworthy:

Provides quick, clear summaries of key concepts.

Simplifies complex topics for better understanding.

Efficient tool for last-minute exam prep.

Enhances retention of crucial information.

Supports effective exam preparation with key points and tips.

Saves time by consolidating information.

Prioritizes important topics and questions.

Offers practical examples for real-world connections.

Boosts student confidence for exams.

Why Choose Vedantu?

In the case of online learning, Vedantu has been a pioneer. The answers provided in the solutions prepared by Vedantu are contributions of skilful experts. Written in easy language, the solutions and notes are understood by the students most easily. Vedantu also prepares for mock tests for students to check their progress. The PDF versions of the solutions are available for free download.

The Revision Notes on Class 9 Science Chapter 4 - Structure of the Atom will help students to have a clear understanding of the concepts covered in this chapter. Students are advised to refer to these notes to secure good marks in the exams. To access other chapters' revision notes and important study materials for Class 9 students, explore Vedantu’s website.

FAQs on Structure of the Atom Class 9 Notes CBSE Science Chapter 4 (Free PDF Download)

1. What is an atomic number? Give one word for the following:

Positively charged atom

A group of atoms carrying a charge

The total number of protons present in the nucleus of an atom is called an atomic number. For Example- atomic numbers of carbon, oxygen, magnesium, and neon are 6, 12, 8, and 10 respectively. 

Positively charged atom - Cation 

A group of atoms carrying a charge – Polyatomic ion.

2. Why are the chemical properties of all isotopes the same? Name the isotopes used in the treatment of cancer and goitre?

Isotopes have the same atomic number, hence the number of the valence electron in them remains the same and this valence electron takes part in the chemical reactions. Thus, isotopes have the same chemical properties. 

Goitre – an isotope of iodine 

Cancer – an isotope of cobalt

3. What is Bohr's structure of atom  Chapter 4 of Class 9 Science?

Bohr's model was presented in the year 1913 by Niels Bohr and Ernest Rutherford. Bohr's model of atoms states that the whole mass of an atom is concentrated as the heavily positively charged nucleus. The atoms consist of electrons that revolve around the nucleus. The electrons revolve around a circular path known as orbits which are also known as energy levels. Every energy level has different amounts of energy. This change in energy takes place when one electron jumps from one energy to another.

4. What is an atom?

Atoms are elements that help create matter. They are the tiniest element available that cannot be further divided. It is the smallest unit of matter that consists of some sort of chemical element. Atoms don't exist independently, instead, they form molecules and ions. These molecules and ions combine together in a huge number which later forms into matter that we can feel, see, and touch. Examples of atoms include Hydrogen, Sodium, Oxygen, and many more.

5. What are the important concepts in  Chapter 4 of Class 9 Science?

Class 9 Science Chapter 4 is titled Structure of the atom. This is an important chapter in Class 9 science as it will help you understand the basics of the chapter for your future studies. Some of the important concepts in this chapter include the structure of an atom, charged particles in matter, mass number, isobars, isotopes, atomic number, valency, distribution of electrons in different orbits, neutrons, Rutherford model of an atom, Thomson's model of an atom, and even Bohr's model of an atom.

6. Where can I find notes for Chapter 4 of Class 9 Science?

Vedantu provides easy Revision notes for Class 9 Science Chapter 4. These notes are explained in detail for you to understand the chapter better, free of cost. There are important concepts and topics that are covered in the notes provided. The notes are also available on the Vedantu Mobile app. This chapter has a good weightage from the examination point of view. Therefore, it is important for you to understand this chapter. 

7. Briefly explain the Cathode Ray Experiment.

The Cathode Ray Experiment refers to the discovery of electrons which was discovered by J. J. Thomson. He was able to discover this by using the cathode-ray tube. A cathode ray tube refers to a vacuum-sealed tube with an anode and a cathode on one end. This created a beam of electrons that were travelled to the other side of the tube. The experiment stated that an atom is an indivisible and simple particle that has at least one electron. 

STUDY MATERIALS FOR CLASS 9

NCERT Solutions for Class 6, 7, 8, 9, 10, 11 and 12

Lakhmir Singh And Manjit Kaur Chemistry Class 9 Solutions

Detailed, Step-by-Step Lakhmir Singh Chemistry class 9 solutions with questions solved by Expert Teachers as per NCERT (CBSE) Book guidelines. Download Now. Formulae Handbook for Class 9 Maths and Science

Here is the list of chapters for Class 9 Lakhmir Singh and Manjit Kaur Chemistry Textbook

• Chapter 1 Matter in Our Surroundings
• Chapter 2 Is Matter Around Us Pure?
• Chapter 3 Atoms and Molecules
• Chapter 4 Structure of the Atom

CBSE Class 9 Resources:

• NCERT Solutions for Class 9 Maths
• NCERT Solutions for Class 9 Science
• RD Sharma Class 9 Maths Solutions
• CBSE Sample Papers For Class 9

FAQs for Lakhmir Singh and Manjit Kaur Solutions

1. Can I read Lakhmir Singh Solutions for Class 9 Chemistry?

Yes, CBSE students of Class 9 can prepare Lakhmir Singh books solutions for Chemistry board exam preparation. It helps you to understand the Chemistry concepts very easily & effectively.

2. Where can I get Lakhmir Singh Class 9 Chemistry Solutions Books Chapterwise?

You will find the best books for Lakhmir Singh Class 9 Chemistry Solutions from our site learncbse.in or else you can avail them via online stores.

3. What are the question types utilized in Lakhmir Singh textbooks to explain Class 9 Chemistry concepts?

Below are the question types that are included in the Lakhmir Singh Class 9 Solutions to explain the questions:

• Very short answer type questions
• Short answer type questions
• Long answer type questions
• Multiple-choice questions
• Questions based on higher-order thinking skills (HOTS)

4. How can I download Solutions for Lakhmir Singh Class 9 Chemistry in PDF?

You can access the available quick links from our page and download Lakhmir Singh Class 9 Chemistry in Pdf format for free of cost.

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Class 9 Science Assignments

We have provided below free printable Class 9 Science Assignments for Download in PDF. The Assignments have been designed based on the latest NCERT Book for Class 9 Science . These Assignments for Grade 9 Science cover all important topics which can come in your standard 9 tests and examinations. Free printable Assignments for CBSE Class 9 Science , school and class assignments, and practice test papers have been designed by our highly experienced class 9 faculty. You can free download CBSE NCERT printable Assignments for Science Class 9 with solutions and answers. All Assignments and test sheets have been prepared by expert teachers as per the latest Syllabus in Science Class 9. Students can click on the links below and download all Pdf Assignments for Science class 9 for free. All latest Kendriya Vidyalaya Class 9 Science Assignments with Answers and test papers are given below.

Science Class 9 Assignments Pdf Download

We have provided below the biggest collection of free CBSE NCERT KVS Assignments for Class 9 Science . Students and teachers can download and save all free Science assignments in Pdf for grade 9th. Our expert faculty have covered Class 9 important questions and answers for Science as per the latest syllabus for the current academic year. All test papers and question banks for Class 9 Science and CBSE Assignments for Science Class 9 will be really helpful for standard 9th students to prepare for the class tests and school examinations. Class 9th students can easily free download in Pdf all printable practice worksheets given below.

Topicwise Assignments for Class 9 Science Download in Pdf

Advantages of Class 9 Science Assignments

• As we have the best and largest collection of Science assignments for Grade 9, you will be able to easily get full list of solved important questions which can come in your examinations.
• Students will be able to go through all important and critical topics given in your CBSE Science textbooks for Class 9 .
• All Science assignments for Class 9 have been designed with answers. Students should solve them yourself and then compare with the solutions provided by us.
• Class 9 Students studying in per CBSE, NCERT and KVS schools will be able to free download all Science chapter wise worksheets and assignments for free in Pdf
• Class 9 Science question bank will help to improve subject understanding which will help to get better rank in exams

Frequently Asked Questions by Class 9 Science students

At https://www.cbsencertsolutions.com, we have provided the biggest database of free assignments for Science Class 9 which you can download in Pdf

We provide here Standard 9 Science chapter-wise assignments which can be easily downloaded in Pdf format for free.

You can click on the links above and get assignments for Science in Grade 9, all topic-wise question banks with solutions have been provided here. You can click on the links to download in Pdf.

We have provided here topic-wise Science Grade 9 question banks, revision notes and questions for all difficult topics, and other study material.

We have provided the best collection of question bank and practice tests for Class 9 for all subjects. You can download them all and use them offline without the internet.

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Selina Solutions Concise Chemistry Class 9 ICSE

2025 syllabus.

• ICSE Class 9
• Class 9 Selina Solutions
• Selina Solution for class 9 Chemistry
• Chapter 4 Atomic Structure And Chemical Bonding

ICSE Selina Solution for Class 9 Chemistry Chapter 4: Atomic Structure and Chemical Bonding

Icse selina solution for class 9 chemistry chapter 4 – free pdf download.

ICSE Selina Solution for Class 9 Chemistry Chapter 4 Atomic Structure and Chemical Bonding provided here guides students in their ICSE Class 9 examination. This study material assists students in understanding the concepts completely by providing an insightful answer to all the exercise questions provided in ICSE Class 9 Selina publications textbook.

Selina Solutions for class 9 Chemistry is an important resource material since it deals with the basic topics of atomic structure and chemical bonding. This chapter is very critical to understand the Physical Chemistry topics in your higher studies.

ICSE Concise solutions provided here sheds light on the structure of an atom, mass number, atomic number, Octet rule. This solution helps you to understand constituents of atoms, electron distribution in orbits, electrovalent and covalent bonding.

Important topics covered in ICSE Selina Solution for Class 9 Chemistry Chapter 4

• Definition of an Atom
• Discovery of an atom
• Discovery of Protons
• Discovery of Nucleus
• Bohr’s Atomic Model
• Discovery of Neutrons
• Structure of Atom
• Atomic Number
• Distribution of Electrons in the Orbits- Bohr-Bury Scheme
• Valence Electrons
• Reason for the chemical activity of an Atom
• Ionic Electrovalent) Bond
• Covalent (Molecular) Bond

Download PDF of ICSE Selina Solution for Class 9 Chemistry Chapter 4 Atomic Structure and Chemical Bonding

Access Answers to Selina publication ICSE Class 9 Chemistry Chapter 4 Atomic Structure and Chemical Bonding

Exercise:4 A

1. What is the contribution of the following in Atomic structure?

a) Maharshi Kanada (b) Democritus?

a) Maharshi Kanada gave the idea of the smallest units of matter. According to him, matter consisted of indestructible minute particles called paramanus, which are now called atoms. He also gave the concept of the molecule.

b) Democritus called the paramanu as an atom, which is derived from the Greek word atomos, meaning indivisible.

2. State Dalton’s atomic theory.

Dalton atomic theory states that atoms are indivisible particles which are the fundamental building blocks of matter. He states that the existence of different types of matter is due to different types of atoms.

Main postulates of Dalton’s atomic theory:

• Matter consists of very small and indivisible particles called atoms.
• Atoms can neither be created nor be destroyed.
• The atoms of an element are alike in all respects, but they differ from the atoms of other elements.
• Atoms of an element combine in small numbers to form molecules.
• Atoms of one element combine with atoms of another element in a simple ratio to form molecules of compounds.
• Atoms are the smallest units of matter which can take part in a chemical reaction.

3. What is an α (alpha) particle?

A doubly charged helium ion (He2+) containing two protons and two neutrons is called an α-particle. α (alpha) particle is formed by removing two electrons from the helium atom.

4. What are the cathode rays? How are these rays formed?

Rays that originate from the negative plate (Cathode) and travel towards anode are called cathode rays.

Formation of cathode rays

When a high voltage charge from an induction coil is applied to tubes filled with gases at very low pressure (0.01 mm of mercury), the gases become good conductors of electricity and begin to flow in the form of rays, which are cathode rays.

5. What is the nature of a charge on (i) cathode rays (ii) anode rays?

Cathode rays are negatively charged as they are made of negatively charged particles.

Anode rays are positively charged as they are made of positively charged particles.

6. How are X-rays produced?

X- rays are produced when a beam of cathode rays is made to fall upon hard metallic targets like tungsten.

7. Why were anode rays also called as ‘canal rays’?

In discharge tube experiment set of rays travelling in a direction opposite to that of the cathode rays were found. These were called canal rays because they passed through the holes or canals in the cathode.

8. How do cathode rays differ from anode rays?

9. State one observation which shows that atom is not indivisible.

Chadwick discovered neutral particles present in an atom by bombarding light nuclei like beryllium with alpha particles. This observation shows that the atom is divisible.

10. a) Name an element which does not contain neutron.

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

a) Hydrogen does not contain neutron.

b) If an atom contains one electron and one proton, it will be neutral in charge.

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

According to Thomson’s atomic model, an atom is made of positively charged substances in the form of a sphere. Electrons are embedded into this sphere, and the total positive charge of the sphere is equal to the total negative charge of electrons, and hence, the atom remained electrically neutral.

12. Which sub-atomic particle was discovered by

(a) Thomson (b) Goldstein (c) Chadwick.

a. Thomson discovered electrons.

b. Goldstein discovered protons.

c. Chadwick discovered neutrons.

13, Name the sub-atomic particle whose charge is

a) +1 (b) —1 (c) 0. 14.

b. Electron

14. (a) Which metal did Rutherford select for his a particle scattering experiment and why ?

(b) What do you think would be the observation of a-particle scattering experiment is carried out on

(i) heavy nucleus like platinum (ii) light nuclei like lithium.

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

b) i) If metal with a heavy nucleus is used for a-particle scattering experiment observation would be same as the original experiment.

ii) If light metal like lithium is used for a-particle scattering experiment, then massive alpha particles will push the nucleus and may not be deflected back.

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

Based on Rutherford’s model of an atom, which subatomic particle is present in the nucleus is the  proton.

16. Which part of the atom was discovered by Rutherford?

Rutherford discovered the nucleus.

17. How was it shown that the atom has empty space?

Rutherford performed an experiment by allowing a stream of alpha particles to pass through a very thin gold foil. He observed that alpha particles pass through the metal foil without deviating from their path. This shows that an atom contains a large empty space called nuclear space.

18. State one major drawback of Rutherford’s model.

The comparison of electrons with planets in the solar system is the main drawback of Rutherford’s model. Thus Rutherford’s model failed to explain the stability of an atom.

19. In the figure given alongside :

(a) Name the shells denoted by A, B and C. Which A shell has the least energy?

(b) Name X and state the charge on it.

(c) The above sketch is of the model of an atom.

a)  A is for K shell or I shell.

B is for L shell or II shell.

C is for M shell or III shell.

Shell K has a minimum amount of energy.

b) X is a nucleus, it is positively charged.

c)  The above figure is of the Bohr model of an atom

20. Give the postulates of Bohr’s atomic model.

Postulates of Bohr’s atomic model are as follows

i) The electrons revolving around the nucleus are confined to certain fixed orbits called shells or energy levels, each of which is associated with a fixed amount of energy.

ii) Electron neither loses nor gain electron while moving around the nucleus.

iii) An electron revolving in a particular orbit, on gaining a certain amount of energy, jumps to the next orbit and vice verse.

Exercise:4 B

1. (a) Name the three fundamental particles of an atom.

(b) Give the symbol and charge of each particle. 2, Complete the table given below by identifying P, Q, R and S.

a) Electrons, protons and neutrons are the three fundamental particles of an atom.

2. Complete the table given below by identifying P, Q and R

3. The atom of an element is made up of 4 protons, 5 neutrons and 4 electrons. What are its atomic number and mass number ?

Atomic number = Number of protons or number of electrons = 4

Mass number = Number of protons + Number of neutrons = 4 + 5 = 9

4. The atomic number and mass number of sodium are 11 and 23 respectively. What information is conveyed by this statement?

Atomic number (11) of sodium conveys information that the number of protons and electrons is the same.

Mass number (23) of sodium indicates the sum of protons and neutrons.

5. Write down the names of the particles represented by the following symbols and explain the meaning of superscript and subscript numbers attached.

n = neutron

e = electron

Top Superscript number: These superscript numbers show their mass number

Bottom Subscript number: These numbers show their atomic number

6. From the symbol \(\begin{array}{l}_{24}^{12}\textrm{Mg}\end{array} \) state the mass number, the atomic number and electronic configuration of magnesium.

Mass number = 24

Atomic number = 12

No. of electrons = 24 – 12 = 12

Electronic configuration = 2, 8, 2

7. Sulphur has an atomic number 15 And mass number of 32.

State the number of protons and neutron in the nucleus of sulphur. Give a simple diagram to show the arrangement of electrons in an atom of sulphur.

Atomic number = 16

Atomic mass = 32

Number of protons = 16

Number of electrons = 16

Number of neutrons = 32 – 16 = 16

Electronic configuration = 2, 8, 6

8. Explain the rule according to which electrons are filled in various energy levels.

i) The maximum capacity of a shell to accommodate electrons is given by the general formula 2n 2 , where n is the serial number of a shell.

ii) The maximum number of electrons possible in the outermost shell is 8, and that in the penultimate shell is 18.

iii) It is not necessary for an orbit to become completed before another is formed. In fact, a new orbit is formed when the outermost shell attains 8 electrons.

9. Draw the orbital diagram Ca +2 ion and state the number of three fundamental particles present in it

Number of three fundamental particles of Ca2+:

Protons: 18

Electrons: 18

Neutrons: 40 – 18 = 22

10. Write down the electronic configuration of the following:

a) \(\begin{array}{l}_{27}^{13}\textrm{X}\end{array} \)

b) \(\begin{array}{l}_{35}^{17}\textrm{Y}\end{array} \)

Write down the number of electrons in X and neutrons in Y.

• Electronic configuration: 2, 8, 3 <Number of electrons = 13Number of neutrons= 27-13= 14
• Electronic configuration: 2, 8, 7Number of electrons = 17Number of neutrons= 35-17= 18

Exercise:4 C

1. How does the Modern atomic theory contradict and correlate with Dalton’ s atomic theory?

The latest research on the atom has proved that most of the postulates of Dalton’s atomic theory contradict. However, Dalton was right that atoms take part in chemical reactions.

Comparisons of Dalton’s atomic theory with the modern atomic theory.

Dalton’s atomic theory:

• Atoms are indivisible.
• Atoms of the same element are similar in every respect.
• Atoms combine in a simple whole-number ratio to form molecules.
• Atoms of different elements are different.

Modern atomic theory:

• Atoms are divisible and consist of electrons, protons, neutrons and even more sub-particles.
• Atoms of the same element may differ from one another.
• Atoms of different elements may be similar called isobars.
• Atoms combine in a ratio which is not a simple whole-number ratio; e.g. in sugar, the C 12 H 22 O 11  ratio is not a whole number ratio.

2. a) What are inert elements?

b) Why do they exist as monoatoms in molecules?

c) What is the valence electron?

a) Elements whose outermost orbital is completely filled are known as inert elements.

b) Inert elements exist as monoatoms because molecules of these elements contain only one atom.

c) Electron present in the outermost orbital os known as valence electrons.

3. In what respect do the three isotopes of hydrogen differ ? Give their structures.

The three isotopes of hydrogen differ in mass numbers which are 1,2 and 3 respectively known as protium, deuterium and tritium.

4. Match the atomic numbers 4. 14. 8. 15. and 19 with each of the following :

(a) A solid non-metal of valency 3.

(b) A gas of valency 2.

(c) A metal of valency 1.

(d) A non-metal of valency 4.

5. Draw diagrams representing the atomic structures of the following

(a) Sodium atom (b) Chloride ion

(c) Carbon atom (d) Oxide ion.

6. What is the significance of the number of protons found in the atoms of different elements?

The number of protons in the nucleus of an atom determines the element type of the atom.

7. Elements X, Y and Z have atomic numbers 6, 9 and 12 respectively. Which one :

(a) forms an anion (b) forms a cation

(c) has four electrons in its valence shell?

a) Y(2, 7) forms an anion.

b) Z(2, 8, 2) forms a cation.

c) X(2, 4) has four electrons in the valence shell.

8. Element X has electronic configuration 2, 8, 18, 8, 1. Without identifying X,

• Predict the sign and charge on a simple ion of X.
• Write if X will be an oxidising agent or reducing agent. Why?

b) The oxidising agent, because it can donate electrons.

9. Define the terms :

a) mass number (b) ion c) cation

d) anion (e) element f) orbit.

a) The mass number is the sum of protons and neutrons present in the nucleus of an atom.

b) An ion is an atom carrying charge due to gaining or losing electrons

c) Positively charged ion which is formed after losing an electron is called a cation.

d) Negatively charged ion formed after gaining an electron is called anion

e) An element  is a substance which cannot be split up into two or more simple substances by usual chemical methods of applying heat, light or electric energy

f) The circular path around the nucleus in which electrons of the atom revolve.

10. From the symbol \(\begin{array}{l}_{4}^{2}\textrm{He}\end{array} \) for the element helium, write down the mass number and the atomic number of the element

Atomic number = 2

Mass number = 4

11. Five atoms are labelled A to E.

(a) Which one of these atoms:

(i) contains 7 protons

(ii) has electronic configuration 2 7.

(b) Write down the formula of the compound forme: between C and D.

(c) Predict : (i) metals (ii) non-metals.

Atom E contains 7 protons.

Atom B has an electronic configuration 2, 7.

b. Atom C stands for  7 Li 3 , Atom D stands for  8 O 16 .

Hence, the compound formula is Li 2 O.

c. Metals: A and C, Non-metals: B, D, E

12. An atom of an element has two electrons in the M she What is the (a) atomic number (b) number of protons in this element?

Number of electrons in the M shell = 2

hence, the number of electrons in the K and L shells will be = 2, 8

Hence, atomic number = 2 + 8 + 2 = 12

Number of protons = 12

13. \(\begin{array}{l}_{24}^{12}\textrm{Mg}\end{array} \) and \(\begin{array}{l}_{26}^{12}\textrm{Mg} \end{array} \) are symbols of two isotopes of magnesium

(a) Compare the atoms of these isotopes with respect to :

(i) the composition of their nuclei.

(ii) their electronic configurations.

(b) Give reasons why the two isotopes of magnesium have different mass numbers.

Hence, composition of nuclei

ii). Electronic configuration = 2, 8, 2

b) Mass numbers of isotopes of Magnesium are different because of the different number of neutrons, i.e. 12 and 14, respectively.

14. What are nucleons? How many nucleons are present in phosphorus? Draw its structure.

Constituents of the nucleus are called nucleons, i.e. protons and neutrons.

The atomic mass of phosphorus = 31

Atomic number = 15

15. What are isotopes? With reference to which fundamental particle do isotopes differ ? Give two uses of isotopes.

Isotopes are the elements having the same atomic number but different mass numbers. Isotopes differ concerning neutrons.

Uses of isotopes

• Some isotopes are radioactive, and they are used to treat cancer Ex: cobalt isotopes
• An isotope of 235U is used as a fuel in a nuclear reactor.

16. Why do \(\begin{array}{l}_{35}^{17}\textrm{Cl} \end{array} \) and \(\begin{array}{l}_{37}^{17}\textrm{Cl} \end{array} \) have the same chemical properties? In what respect do these atoms differ?

Electrons are the particles which take place in reaction. Chemical properties depend on the electronic configuration. In isotopes of \(\begin{array}{l}_{35}^{17}\textrm{Cl} \end{array} \) and \(\begin{array}{l}_{37}^{17}\textrm{Cl} \end{array} \) the atomic numbers are the same; hence, their electronic configuration remains the same, and so are their chemical properties.

These differ only in physical contents and weights because neutrons contribute to the mass of an atom which is 35 and 37 in this case.

17. Explain fractional atomic mass. What is the fractional mass of chlorine?

Fractional atomic mass is the weighted average of all the naturally occurring isotopes of that element. Fractional mass of chlorine is 35.5.

18. a) What is meant by “ atomic number of an element”?

b) Complete the table given below:

Write down the electronic configuration of i) Chlorine atom ii) Chloride ion

• The number of protons in the nucleus of an atom represents atomic number of an element.

c) i. Electronic configuration of chlorine = 2, 8, 7

ii. Electronic configuration of chlorine ion = 2, 8, 8

19. Name the following:

(a) The element which does not contain any neutron in its nucleus.

(b) An element having valency `zero’.

(c) Metal with valency

(d) Two atoms having the same number of protons and electrons but a different number of neutrons.

(e) The shell closest to the nucleus of an atom.

a) Hydrogen

c) Magnesium

d) Hydrogen and carbon

20. Give reasons

(a) Physical properties of isotopes are different

(b) Argon does not react.

(c) Actual atomic mass is greater than mass number.

(d) \(\begin{array}{l}_{35}^{17}\textrm{Cl} \end{array} \) and \(\begin{array}{l}_{37}^{17}\textrm{Cl} \end{array} \) and do not differ in their chemical reactions.

a) Physical properties are a dependent atomic mass of an element. Isotopes have different atomic mass hence they differ in their physical properties.

b) Arong outermost orbital is completly filled with 8 electrons. Hence, it does not react.

c) Actual atomic mass is greater than the mass number because the mass number is a whole number approximation of atomic mass unit.

d) \(\begin{array}{l}_{35}^{17}\textrm{Cl} \end{array} \) and \(\begin{array}{l}_{37}^{17}\textrm{Cl} \end{array} \) and do not differ in their chemical reactions their atomic mass determines the chemical reactivity. Here chlorine isotose have the same mass number.

21. An element A atomic number 7 mass number 14

B electronic configuration 2, 8, 8

C electrons 13, neutrons 14

D Protons 18 neutrons

E electronic configuration 2, 8, 8, 1

State (i) valency of each element (ii) which one is a metal (iii) which is a non-metal (iv) which is an inert gas.

Atomic number = 7 = Number of electrons = 2, 5

Valency of A = 8 – 5 = 3

Electronic configuration 2, 8, 8

Valency of B = Zero

Element C has 13 electrons

Electronic configuration = 2, 8, 3

Valency of C = 3

Protons = 18 = Electrons = 2, 8, 8

Valency of D = Zero

Electronic configuration = 2, 8, 8, 1

Valency of E = 1

(ii) C and E are metals.

(iii) A is a non-metal.

(iv) A, C and E are not inert gases.

22. Choose the correct option

(a) Rutherford’s alpha-particle scattering experiment discovered

A. Electron

C. Atomic nucleus

(b) Number of valence electrons in 0 -2 is :

(c) Which of the following is the correct electronic configuration of potassium ?

C. 2, 8, 8, 1

D. 1, 2, 8, 8

(d) The mass number of an atom whose unipositive ion has 10 electrons and 12 neutrons is :

a) C.Atomic nucleus

23. Explain : (a) octet rule for formation of a chemical compund. (b) duplet rule for formation of hydrogen.

a) Atoms of all noble gases have eight electrons in their outermost shell. This arrangement is called an Octet configuration. Each element tends to combine to attain electronic compounds either by obtaining or donating and sharing of electrons present in their outermost shell. This rule of attaining octet configuration is called as octet rule.

b) Hydrogen atom has one electron in the valence shell which it shares with another hydrogen atom having one electron to complete its duplet state, i.e. two electrons in the valence shell and resulting in the formation of hydrogen.

24. Complete the following table relating to the atomic structure of some elements.

Exercise :4 D

1• How do atoms attain noble gas configuration?

Atoms attain noble gas configuration either by obtaining or donating and sharing of electrons present in their outermost shell.

2• Define electrovalent bond.

The chemical bond formed due to the electrostatic force of attraction between cation and anion is called an electrovalent bond.

3. Elements are classified as metals, non-metals, metalloids and inert gases. Which of them form electrovalent bond?

Metals tend to lose electron; hence, they combine with nonmetals to form electrovalent bond.

4.(a) An atom X has three electrons more than the noble gas configuration. What type of ion will it form?

(b) Write the formula of its (X) (i) sulphate (ii) nitrate (iii) phosphate (iv) carbonate (v) hydroxide.

a) An atom X which has three electrons more than the noble gas configuration loses 3 electrons to form cation.

b)  i. X(SO 4 ) 3

ii. X(NO 3 ) 3

iv. X 2 (CO 3 ) 3

5. Mention the basic tendency of an atom which makes it to combine with other atoms.

Atoms tend to become stable and for them attaining stability is nothing but obtaining an electronic configuration of inert gas. Helium has two atoms in its outermost orbitals whereas other inert gases like neon, argon, krypton, xenon and radon have eight electrons (octet) in the outermost shell.

6. What type of compounds are usually formed between metals and non-metals and why?

Metals and nonmetals usually combine to form an electrovalent bond because metallic elements which have 1, 2 or 3 valence electrons tend to lose electrons and non-metallic elements which have 5, 6 or 7 valence electrons tend to receive electron.

7. (a) In the formation of the compound XY 2 , an atom X gives one electron to each Y atom. What is the nature of bond in XY 2 ?

(b) Draw the orbit structure of this compound (XY 2 ).

a) Nature of bond in XY 2  is an ionic bond.

b) Orbit structure of XY 2

8. An atom X has electronic configuration 2,8,7. It combines with Y having 1 electron in its outermost shell.

(a) What type of bond will be formed between X and Y?

(b) Write the formula of the compound formed.

a) Ionic bond

9. Draw orbit structure diagram of

• Sodium chloride (NaCl) b) Calcium Oxide (CaO)

[Atomic numbers Na= 11, Ca=20, Cl= 17, O=8]

10. Compare :

(a) sodium atom and sodium ion

(b) chlorine atom and chloride ion, with respect to

(i) atomic structure, (ii) electrical state

11. The electronic configuration of fluoride ion is the same as that of a neon atom. What is the difference between the two ?

Fluoride ion is a negatively charged ion with 9 protons and 10 electrons, whereas Neon atom is electrically neutral with 10 protons and 10 electrons.

12. (a) What do you understand by redox reactions?

(b) Explain oxidation and reduction in terms of loss or gain of electrons.

a) In redox reaction, there is the transfer of electrons, which results in the bond formation. The electropositive atom undergoes oxidation, while the electronegative atom undergoes reduction.

b) Oxidation is a process in which an atom or ion looses electrons. The reduction is a process in which an atom or ion gains electrons.

13. Potassium (at No. 19) and chlorine (at No. 17) form a compound. Explain the formation of the compound on the basis of (a) oxidation (b) reduction (c) oxidising agent (d) reducing agent.

2K + Cl 2  → 2KCl

a) Oxidation : In the electronic concept, oxidation is a process in which an atom or ion loses an electron(s).

K → K +  + e –

b) Reduction:  In the electronic concept, reduction is a process in which an atom or ion accepts electron(s).

Cl 2  + 2e – → 2Cl –

c) Oxidising agent

An oxidising agent oxidises other substances either by accepting electrons or by providing oxygen or an electronegative ion, or by removing hydrogen or an electropositive ion.

d) Reducing agent

A reducing agent reduces other substances either by providing electrons or by providing hydrogen or an electropositive ion, or by removing oxygen or an electronegative ion.

Exercise :4 E Page no: 76-77

1. a) Define covalent(molecular bond).

b) Give an example of covalend bond formed by

i) similar atoms b) dissimilar atoms

a) The bond formed between two atoms by mutual sharing of one or more pair of electrons os called as covalent bonding.

b) i) Bond formed between two Cl atoms; Cl‒Cl

ii) Bond formed between a hydrogen atom and chlorine atom; H‒Cl

2. Covalent bonds can be single, double or triple covalent bond. How many electrons are shared in each? Give an example of each type.

A single covalent bond is formed by sharing of one pair of electrons between atoms; each atom contributes one electron. Ex: Formation of Hydrogen molecules

A double bond is formed by sharing two pairs of electrons between two atoms. Ex: Formation of Oxygen molecule

A triple bond is formed by sharing of three pairs of electrons between two atoms. Ex: Formation of N2 molecules

3. Show number of bonds in

(i) ethene molecule (ii) ethyne molecule

i) Ethene molecule has one double covalent bond and four single covalent bonds.

ii) Ethyne molecule has one triple covalent bond and two single covalent bonds.

4. An element A has 1 electron in its first shell. It combines with clement B having 7 electrons in its third shell. What type of bond is formed ?

Element A with 1 electron in its first shell is hydrogen, and element B with 7 electrons in its third shell is chlorine. So, a single covalent bond is formed between hydrogen and chlorine by sharing one pair of electrons.

5. Match the atomic numbers 4, 8, 10, 15 and 19 with each of the following

(a) Element which can form trivalent ion.

(b) An element with 4 shells.

(c) Element with 6 valence electrons.

(d) Element which does not form ion.

Atomic number 15

Electronic configuration (15): 2,8,5

Atomic number 19

Electronic configuration (19): 2,8,8,1

Atomic number 8

Electronic configuration (8): 2,6

Atomic number 10

Electronic configuration (10): 2,8

6. If electrons are getting added to an element Y; then

(a) is Y getting oxidized or reduced ?

(b) what charge will Y migrate to during the process of electrolysis ?

a) Electrons are getting added to element Y, so, it is getting reduced.

b) Y will migrate towards the positive charge.

7. (a) Elements X, Y and Z have atomic numbers 6, 9 and 12 respectively. Which one

i) forms an anion , (ii) forms a cation,

b) State the type of bond between Y and Z and give, its molecular formula.

Ionic bond with molecular formula ZY 2 .

8. Taking MgCl, as an example of electrovalent bond, CCl 4 as a covalent bond. Give a difference between electrovalent and covalent bonds.

9.Potassium Chloride is an electrovalent compound, while hydrogen chloride is a covalent compound. But, both conduct electricity in their aqueous solutions. Explain.

Ans. : Both have free mobile ions in their aqueous state

In potassium chloride electrostatic forces of attraction weaken in the fused state or in aqueous solution which make them conduct electricity.

Hydrogen chloride is a polar compound which ionise in their solution which act like electrolyte. This will make Hydorgen chloride to conduct electricity.

10. Name two compounds that are covalent when taken pure but produce ions when dissolved in water.

Ans. • Ammonia and HO

HCl and NH 3

11. An element M burns in oxygen to form an ionic compound MO. Write the formula of the compounds formed if this element is made to combine with chlorine and sulphur separately.

12. Give orbital diagram of the following :

(a) magnesium chloride, (b) nitrogen,

(c) methane (d) hydrogen chloride

13. State the type of bonding in the following molecules.

(a) water, (b) calcium oxide, (c) hydrogen chloride

a) Polar covalent bond

b) Ionic bond

c) Polar covalent bond

14. Metal M forms a chloride with the formula MC1 2 . What type of bond in MC12? Write the formula of the compound when M combines with sulphur, oxygen and nitrogen.

The bond formed between metal and nonmetal is ionic bond.

Bond formed between metal M and chlorine is ionic bond.

When metal M combines with sulphur – MgS

When metal M combines with  oxygen – MgO

When metal M combines with nitrogen – Mg 3 N 2 .

15. Explain the following :

(a) Mass of an atom is concentrated inside the nucleus of the atom.

(b) Atoms combine by transfer and sharing of electron(s).

(c) An element has atoms with different mass number,

(d) Carbon-12 and carbon-14 both show chemical properties

a) Mass of an atom is contributed by proton and neutron. An electron has a negligible mass which does not contribute much for the mass of an atom. As protons and neutron lie inside the nucleus mass of an atom is majorly present in the nucleus.

b) Atoms tend to attain a stable electronic configuration. To achieve a stable configuration, they share the electrons present in their valence electrons.

16. Choose the correct answer from the choices A, B, C and D:

(i) The characteristic of an covalent compound is that:

A. they are farmed by sharing of electrons.

B. they are formed between metals and non-metals.

C. they are formed between two non-metals.

D. they often exist as a liquid.

(ii) When a metal atom becomes an ion

A. it loses electrons and is oxidized,

B. it gains electrons and is reduced,

C. it gains electrons and is oxidized,

D. it loses electrons and is reduced

(i) B. They are formed between metals and non-metals.

(ii) A. It loses electrons and is oxidised.

17. Identify the following reactions as either oxidation or reduction:

i) Reduction

ii) Oxidation

iii) Reduction

iv) Oxidation

18. a) Name the charged particles which attract one another to form electrovalent comopounds.

(b) In the formation of electrovalent compounds; electrons are transferred from one element to another. How are electrons involved in the formation of a covalent compound ?

(c) The electronic confi.wration of nitrogen is (2, 5) How many electrons in the outer shell of a nitrogen atom are not involved in the formation of a nitrogen molecule ?

(d) In the formation of magnesium chloride (by direct combination between magnesium and chlorine). Name the substance that is oxidized and the substance that is reduced.

a) Cation and anion

b) By mutual sharing of electrons

d) Magnesium is oxidised and chlorine is reduced.

19. What is the term defined below?

(a) A bond formed by a shared pair of electrons, each bonding atom contributing one electron to the pair.

(b) A bond formed by transfer of electron(s).

a) Single covalent bond

b) Electrovalent bond

20. Name or state the following.

(a) An element having valency zero.

(b) Metal with valency one.

(c) Atoms of the same element differing in mass numbers.

(d) Elements having same mass number but different atomic number.

( e) Bond formed by transfer of electrons (s)

( f) Ion formed by gain of electron(s)

(b) Lithium

(c) Hydrogen

(d)   40 18 Ar and  40 20 Ca

(e) Ionic bond

21. An element X has 2 electrons in its M shell, it forms bond with an element Y which has 7 electrons in its third orbit.

a) Write the formula of the compound formed.

b) Which nearest inert gas electronic configuration will element X and Y acquire?

c) Show by orbital diagram the formation of compound between X and Y.

a) Element X is Mg (12) and element Y is Cl (17) hence the compound formed will is MgCl 2 .

b) The nearest inert gas electronic configuration for element X is 2,8, while that for element Y is 2,8,8.

22. In the formation of i) Oxygen molecule ii) Carbon tetra chloride molecule, state the following.

• Electronic configuration of nearest inert gas attained.
• How many electrons are sahred/transferred in bond formation?
• Which type of bonds these compounds form?
• Draw the orbital diagrams?

In the formation of i) Oxygen molecule

a) Neon (10) 2,8

b) Two pairs of electrons are shared.

c) Covalent bond

d) Orbital Diagram:

In the formation of ii) Carbon tetra chloride molecule

b) Four pair of electrons are shared.

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Frequently Asked Questions on Atomic Structure and Chemical Bonding

State dalton’s atomic theory.

Dalton atomic theory states that atoms are indivisible particles which are the fundamental building blocks of matter. He states that the existence of different types of matter are due to different types of atoms.

What is an α (alpha) particle?

What are cathode rays.

Rays that originate from the negative plate( Cathode) and travels towards anode are called cathode rays.

How are X-rays produced?

Why anode rays also called as ‘canal rays’, which part of atom was discovered by rutherford, how was it shown that atom has empty space , state one major drawback of rutherford’s model.

The comparison of electrons with planets in the solar system is the main drawback of Rutherford’s model. Thus Rutherford’s model failed to explain the stability of an atom.

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