Atomicity

The number of atoms of all the elements present in a molecule of any substance is called its atomicity.

Monatomic molecules.

The molecules which contain only one atom in their molecule are called monatomic molecules.

Examples. Noble gases viz, helium, neon, argon, etc. are monatomic gases. Therefore, the atomicity of helium (He), neon (Ne) and argon (Ar) is one.

Diatomic molecules.

The molecules which contain two atoms in their molecule are called diatomic molecules.

Examples. The molecules of gases like hydrogen, oxygen, nitrogen, chlorine, etc. contain two atoms. Therefore, molecules of hydrogen, oxygen, nitrogen, chlorine are diatomic molecules.

Thus, the atomicity of hydrogen (H₂), oxygen (O₂), nitrogen (N₂) and chlorine

(Cl₂) is two.

Triatomic molecules.

The molecules which contain three atoms in their molecule are called triatomic molecules. Examples. The molecules of water and carbon dioxide are triatomic molecules. Therefore, the atomicity of water (H₂O) and carbon dioxide (CO₂) is three.

The atomicity of

• Ozone is 3

• Phosphorus (yellow) is 4

• Sulphur is 8