ATOMICITY

Atomicity

The number of atoms contained in a molecule of a substance (element or compound) is called its atomicity.

Based upon atomicity we can classify molecules as follows.

1. Monoatomic molecules:  Noble gases like helium, neon, argon, etc., exist in atomic forms, i.e., they are monoatomic. For example, helium, neon and argon exist as He, Ne and Ar respectively.

2. Diatomic molecules: These molecules consist of two atoms. For example, hydrogen (H₂) Oxygen (O₂), Nitrogen (N₂) chlorine (Cl₂), Carbon monoxide (CO), hydrogen chloride (HCl) and sodium chloride (NaCl).

3. Triatomic molecules : These molecules consist of three atoms. For example, ozone (O₃) is a triatomic molecule. Similarly, carbon dioxide (CO₂), nitrogen dioxide (NO₂) and hydrogen sulphide (H₂S) are examples of triatomic molecules.

4. Tetraatomic molecules : These molecules consist of four atoms. For example, P₄ is a tetraatomic molecule of phosphorus.

5. Polyatomic molecules : Any molecule containing more than four atoms is called a polyatomic molecule. For example, sulphur (S₈) methane (CH₄), nitric acid (HNO₃), sulphuric acid (H₂SO₄), ethanol (C₂H₂OH).