NCERT Solutions for Class 9 Science Chapter 4

NCERT Solutions for Class 9 Science Chapter 4: The CBSE Class 9 Science chapter 4 is The Structure of Atom. In this chapter, students will learn about charged particles in a matter, structure of an atom, how electrons are distributed in different orbits, valency, atomic number and mass number, isotopes, etc. The NCERT Solutions for Class 9 Science chapter 4 will help students write comprehensive answers for work on the concepts they find difficult.

Structure of Atoms is an important chapter for students as it will help them build a base for concepts based on it in higher classes. In this article, we have provided the PDF for Class 9 Science chapter 4 for easy download. Students are advised to do answer-writing practice with the help of solutions and use it for revision. Scroll down to learn more about NCERT solutions for Class 9 Science chapter 4.

NCERT Solutions for Class 9 Science: Structure of Atom

The chapter 4 of Science Class 9 deals with the discovery and structure of an atom. Moreover, students will learn the work of famous scientists who developed various models and theories. Before getting into the details of the structure of atom Class 9 NCERT solutions, let us have a look at the topics and sub-topics in this chapter:

NCERT Solutions for Class 9 Science Chapter 4: Free PDF

Students can download the NCERT Solutions for Class 9 Science chapter 4 from the section below:

NCERT Solutions for Class 9 Chapter 4: Solved Questions

Q.1. If bromine atom is in the form of say two isotopes 3579Br 49.7% and 3581Br (50.3%), then calculate the average mass of bromine atom.

Solution: Given, two isotopes of bromine are 3579Br 49.7% and 3581Br (50.3%), Average atomic mass = Atomic mass of 1st isotope×% abundance of isotope100+ Atomic mass of 2nd isotope ×% abundance of isotope 100

Average atomic mass of bromine atom=79×49.7100+81×50.3100
=3926.3100+4074.3100
=80.006 u

Q.2. The average atomic mass of a sample of an element X is 16.2 u. What are the percentages of isotopes 816X and 818X in the sample?

Solution: Average atomic mass is the sum of atomic mass of isotopes, each multiplied by its natural substance. Let the percentage of one of the isotopes in the sample be x, so that the percentage of the other isotope in the sample will be (100-x). Mass of isotope 816X is 16 u and let its percentage be x% . Mass of isotope 818X is 18 u and its percentage be
(100-x)%Average atomic mass = Atomic mass of 1st isotope×% abundance of isotope100+ Atomic mass of 2nd isotope ×% abundance of isotope 100 Average atomic mass
of X=16×x100+18×100-x100 But, the average atomic mass of X is given as 16.2 u Therefore, 16.2=16×x100+18×100-x100
16.2=16×100+1800-18×100
16.2×100=1800-2x
2x=1800-1620
So, x=180/2=90 Percentage of 816X in the sample= 90%
Percentage of 818X in the sample= 10%

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

Solution: Atomic number, Z=3 Distribution of electrons: K=2, L=1
The nearest noble gas is helium with atomic number 2. In order to gain the stable configuration of this element, Z loses one electron from its outermost shell. So, Valency =1
Valency is the combining capacity of an element and is equal to the electrons present in its outermost shell. The element is Lithium.

DOWNLOAD CLASS 9 SCIENCE CHAPTER 4 NCERT SOLUTIONS PDF

CBSE Class 9 Science Chapter 4: Chapter Summary

In this chapter, students will learn about the basic terms involved in the study of an atom, such as atomic number, atomic mass, neutrons, and valency. They will also learn about the different atomic models, their features, and their limitations. The study will start with charged particles in matter, followed by the basic structure of an atom. 

Thomson’s Model of an atom, Rutherford’s Model of an atom, and Bohr’s Model of an atom are explained and the limitations of these models are studied. Students will then know what shells and orbitals are. You will also be introduced to the scientists who have contributed to the study of the atom. Lastly, they will be introduced to the terms – Isotopes and Isobars.

Class 9 Science Chapter 4 Important Questions

Below we have provided some important and additional questions that will help students in their preparation for exams:

Short Answer Type Questions

• Define the following:
  • Atomic Number
  • Mass Number
  • Valency
  • Isotopes
  • Isobars
• On the basis of Thomson’s model of an atom, explain how the atomic neutral as a whole.
• Draw a sketch of Bohr’s model of an atom with three shells.
• If K and L shells of an atom are full, then what would be the total number of electrons in the atom?

Long Answer Type Questions

• For the symbol Hydrogen, Deuterium and Tritum tabulate three sub-atomic particles found in each of them.
• Write the electronic configuration of any one pair of isotopes and isobars.
• Compare the properties of electrons, protons and neutrons.
• How will you find the valency of chlorine, sulphur and magnesium?
• Describe Bohr’s model of the atom.
• Summarise the rules for writing of distribution of electrons in various shells for the first eighteen elements.

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