Lesson 1 (Atomic Structure Basics & Isotopes)

First, let us enjoy this tutorial.






1. Matter is made up of atoms. Atoms themselves are made up of three sub-atomic particles : protons, neutrons and electrons

Particle/ Mass/ Charge

Proton 1 +1

Neutron 1 1 0

Electron 1/1840 -1

2. The protons and neutrons are located at the centre of the atom in the nucleus.

3. Electrons are arranged in shells around the nucleus. The 1st shell can hold a maximum of 2 electrons and the 2nd and 3rd shells can hold a maximum of 8 and 18 electrons respectively.

4.Every element has its own proton number, symbolised by Z, and the nucleon number, symbolised by A.

5. The proton number of an element is the number of protons in its atom. As an atom has to be electrically neutral, the number of electrons is the same as the number of protons.

6. The nucleon number of an element is the total number of protons and neutrons in its atoms.

Eg. The symbol for sodium (Na) is written as

nucleon number (A) --------23

------------------------------------Na

proton no. (Z) --------------11

Thus there are 11 protons, 11 electrons and 12 neutrons.

7. Isotopes are atoms of the same element with different numbers of neutrons.

For example, Cl-35 and Cl-37 are isotopes as they have the same number of protons. They are from the same element. However, they have a different number of neutrons. This difference in the number of neutrons can affect certain physical properties such as boiling point. It does not affect any chemical properties.

In the case of ions, the number of electrons will not be the same as the number of protons as they will lose or gain electrons during formation.

Eg.