What are Different Atomic Species CBSE NCERT Notes for Class 9 Science Chapter 4 Structure Of The Atom

CBSE NCERT Notes for Class 9 Science Chapter 4 Structure Of The Atom​

Chapter 4 Structure of NCERT Solutions for Class 9 Science At skillyogi, the Atom gives students with answers to all of the questions in the NCERT Class 9 textbook, which is aligned with the CBSE board.

This page offers students with study source material that has been compiled by a team of subject-matter experts. Solving NCERT Solutions for Class 9 Science enables students to get the highest score on the CBSE Class 9 Science Term II test.

CBSE Class 9 Science notes will assist students in studying the topic thoroughly and clearly.

These CBSE Class 9 Science notes were written by subject experts who made the study material very basic, both in terms of language and format.

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What are Different Atomic Species?

Different Atomic Species


  1. These are classified as identical atoms of the same element with different mass numbers. For instance, there are three isotopes of the hydrogen atom: protium (4I), deuterium (2H), and tritium ( 31 H).
  2. In other words, isotopes have the same amount of protons but the change in their neutron count. Each element’s isotope is a pure substance.
  3. Due to the fact that the chemical characteristics of elements are highly dependent on their electronic configuration, or outermost electrons, and since isotopes of an element have similar electron configurations, isotopes of an element have comparable chemical properties. 
  4. We are aware that the masses of isotopes of elements vary. Because physical characteristics like density, light scattering, and so on are mass-dependent, they differ across isotopes of an element.

Average Atomic Mass

  1. If an element has no isotopes, the mass of an atom is equal to the sum of the masses of its protons and neutrons.
  2. However, if an element exists in isotopic forms, the average mass is determined as follows:

Average atomic mass of an element [(Atomic mass of isotope I x percentage of isotope I) + (Atomic mass of isotope II x percentage of isotope II)+…] 

The two isotopic forms of chlorine atom with masses 35u and 37u occur in the ratio of 3 : 1. 

Applications of Isotopes

  1. A chemical element of uranium (U-235) is used as a fuel in nuclear reactors to generate energy.
  2. U-238 is used to calculate the age of rock formations and even the world.
  3. A cobalt isotope (Co-60) is used to treat cancer.
  4. Carbon isotopes (C-14) are used to assess the age of old wood specimens and fossilised bones of living animals.
  5. Iodine isotope (I-131) is used to treat goitre.


Isobars are atoms of various elements with various atomic numbers but the same mass number. In other words, isobars are atoms of different elements that share the same amount of nucleons (protons + neutrons) but vary in their proton count. 148Ar  and 204°ca, for example, are isobars.

Due to the fact that isobars have a different atomic number and electrical structure. As a result, their chemical nature is also different.

CBSE Class 9 Science Detailed Notes​

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