AP Board Class 9 Physical Science Chapter 6 What is Inside An Atom?

In previous chapters students will have already learnt about “matter” and that it is made up tiny particles called atoms. However, in AP Board class 9 physical science chapter 6 student will dig deeper into topics like the structure of an atom and learn about what is inside an atom. Students will be introduced to sub-atomic particles and various atomic models that will help them to clearly understand the structure of the atoms. The topics covered in this chapter include;

  • Electrons, Protons and Neutrons
  • Thomson’s Model of Atoms
  • Rutherford’s Model of Atom
  • Bohr’s Model of Atom

Sub-atomic Particles Of An Atom

  1. Negatively charged particles in an atom are known as Electrons.
  2. Protons are positively charged particles present in the atomic nucleus.
  3. Neutron is a particle without any charge but is a part of the atomic nucleus.

Thomson’s Model of Atoms

Thomson’s model basically stated that the atoms contained negatively charged particles. His model showcased electrons embedded throughout the mass of positively charged material.

Rutherford’s Model of Atom

When Rutherford conducted the alpha-particle scattering experiment he discovered the atomic nucleus. However, Ernest Rutherford’s model of the atom showcases large empty spaces with a small, dense and positively charged nucleus at the centre.

Bohr’s Model of the Atom

Neils Bohr was basically a modification to Rutherford’s model of the atom. Bohs’s model stated that electrons moved in specific energy levels throughout the nucleus.

Atomic Number

The number of protons in the nucleus of an atom is called the atomic number.

Mass Number

The mass number is nothing but the total number of protons plus the number of neutrons present in the nucleus.

Students can have a glimpse of chapter questions that are given below to further understand some of the topics.

Question 1: Who discovered electron and neutron?

Answer: The credit for the discovery of electron and neutron has been given to J.J. Thomson and J. Chadwick respectively.

Question 2: Define; i. Valency ii. Isotopes


i. Valency is the combining capacity of an atom.

ii. Isotopes are atoms which have the same number of protons, but a different number of neutrons

Question 3: What did Rutherford’s alpha-particle scattering experiment result in?

Answer: Rutherford’s alpha-particle scattering experiment led to the discovery of the atomic nucleus.

Do stay tuned to BYJU’s to learn more about class 9 science topics and access various Andhra board study materials including syllabus, exam timetable and more.

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Practise This Question

The atomicity of FeCO3 is