Lakhmir Singh Chemistry Class 9 Solutions Structure Of The Atom (Chapter 4)

Lakhmir Singh Chemistry Class 9 Solutions for Chapter 4 plays an important part in the exam preparation. Chemistry is a tough subject but if you sincerely study each chapter of Class 9 Chemistry, you can easily score well in the CBSE exams.

There are 9 exercises in this chapter. The chapter of Lakhmir Singh Solutions, ‘Structure of Atoms’ is introduced to tell you everything about an atom. As you have learned in the earlier chapters that atoms and molecules are the only building block of matter. It is essential to understand the internal structure of atoms to see how things work.

In this chapter, we will learn about What makes the atom of one element different from the atom of another element. Are atoms indivisible? Also, you will learn about subatomic particles and different models that explain the particles that are arranged within an atom. The chapter covers various topics along with detailed solutions like the charged particles in matter, the structure of an atom, different models, how electrons are distributed in an atom, valency, atomic and mass number, isotope, isobars, etc. 

Topics covered under Lakhmir Singh and Manjit Kaur Solutions Class 9 Chapter 4

Chapter 4 of Class 9 Chemistry deals with different topics that amazingly explain to you everything about the structure of an atom. It was a challenge for scientists to reveal the structure of the atom. 

Charged Particles in Matter

This topic will teach you how matter contains charged particles. When you rub two objects together, they electrically get charged. The question is where does this charge come from? You will know that an atom is indivisible and it contains charged particles. 

Structure of an Atom

To tell the structure of the atom, there are different models that explain the structure in different ways in this chapter. 

Thomson’s Model of an Atom

This model stated that in a sphere of positive charge, the electrons are divided like currents in a spherical Christmas pudding. This model proposed that:

  • Atoms have a positively charged sphere carrying electrons. 
  • Also, the negative and positive charges are equal in magnitude. 

Rutherford’s Model of an Atom

Rutherford carried out an experiment to explain the structure of an atom. You need to go through the chapter to know how he explained the structure. But he concluded that:

  • There is a positively charged center in an atom that is known as a nucleus. All the mass in an atom resides in the nucleus. 
  • The electrons revolve around the nucleus in well-defined orbits. 
  • Also, the size of the nucleus is quite smaller than the size of an atom. 

Bohr’s Model of an atom

This model stated that:

  • Only certain orbits are known as discrete orbits of electrons.
  • Also, while the electrons revolve in the discrete orbits, they do not radiate energy. 


Neutron refers to a subatomic particle that has no charge and has a mass nearly equal to that of a proton. 

How are the Electrons are distributed in different shells?

This topic is going to explain to you how and in which orbit the electrons are more. Also, you will know about the valence electrons. How much they are or how they are divided in that particular shell. 

Atomic Number and Mass Number

The atomic number is referred to as the total number of protons present in the nucleus of an atom. Now, to know about protons, you need to understand the chapter. Similarly, you will be guided on mass numbers. These topics cover different aspects that are essential for you to understand thoroughly. 

The other topics covered in the chapter are isotopes and isobars. 

Exercise Wise Discussion of Class 9 Chemistry Chapter 4: Structure of an Atom

This chapter covers 9 exercises in which you will have to answer several questions based on the topic of the chapter. Below is how much questions are there in different sets of exercises:

Exercise 1 (Page 191)

This exercise has 11 questions in total which are one-word answers. These questions are from the entire chapter.

Exercise 2 (Page 192)

This set of exercises has 23 questions with some true or false questions, fill in the blanks and one-word answers along with some reasoning questions. 

Exercise 3 (Page 193)

This exercise set has 24 questions based on the different models of the atom along with some numerical questions in which you have to find the number of electrons, protons or neutrons along with the atomic number and mass number. 

Exercise 4 (Page 194)

This exercise has only four questions in which you are given different situations that ask you to find several things under one category. 

Exercise 5 (Page 195)

This exercise has only 2 questions which are numerical. 

Exercise 6 (Page 210)

This exercise has 18 questions which are a mixture of numerical, fill in the blanks, definitions, etc. 

The three other exercises cover more than 20 questions that cover different other topics of the chapter. If you solve all the exercises easily, then you have understood the chapter well. But if not, the Instasolv team is there for you. 

Benefits of Lakhmir Singh and Manjit Kaur Solutions Class 9 Chemistry Chapter 4

  • Lakhmir Singh Chemistry Class 9 Solutions for Chapter 4 is introduced to clear your concept of the atom. 
  • We have the Chemistry experts who dedicatedly work to solve all your doubts regarding the chapter. 
  • From basic questions too difficult numerical, we will answer you all. 
  • Thus, to score good marks in your examination, you need to understand the chapter well.