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

In previous chapters, students will have already learnt about â€śmatterâ€ť 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
• Thomsonâ€™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.

### Thomsonâ€™s Model of Atoms

Thomsonâ€™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. Bohsâ€™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.

Question 4: What is atomic number?

Answer:Â Atomic number is the number of protons in the nucleus of an atom.

Question 5: Which are the three sub-atomic particles of an atom?

Answer:Â The three sub-atomic particles of an atom are: (i) electrons, (ii) protons and (iii) neutrons.

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