Question

What is meant by atomicity of a molecule?

Answer 1

Hint: Atomicity of a hydrogen molecule ($H_2$ ) is two while atomicity of ozone molecule ($O_3$) is three. Atomicity of a molecule can be classified into: Monoatomic, diatomic, triatomic, triatomic and polyatomic.

Complete step by step answer:
Atomicity of a molecule can be defined as a measure of the total number of atoms present in a molecule of an element. For example, an ozone molecule (written as $O_3$) consists of three atoms of oxygen and hence its atomicity is 3. Similarly, for hydrogen molecule atomicity is two because it contains two hydrogen atoms.

Atomicity can be classified into:
- Monoatomic: Molecules of elements which contain only a single atom of that element are termed as monatomic and thus atomicity of these molecules is one. For example, Argon (Ar), Helium (He), having atomicity as one.
- Diatomic: Molecules of elements that are composed of two atoms of that element are termed as diatomic. Diatomic molecules have atomicity equals to two. For example, an oxygen molecule ($O_2$ ) is diatomic and hence its atomicity is two.
- Triatomic: Molecules of elements that are composed of three atoms of that element are termed as triatomic. Since, these molecules are composed of three atoms, they have atomicity equal to three. For example, $O_3$, having atomicity as three.
- Tetratomic: Molecules of elements that are composed of four atoms of that element are termed as tetratomic. For example, phosphorus molecules ($P_4$) , having atomicity equals to 4.
- Polyatomic: Molecules of elements that are composed of more than four atoms of that element are termed as polyatomic. For example, sulphur ($S_8$) is a polyatomic molecule and has atomicity equals to 8.

Note: It should be noted that atomicity has no relation with the valency of an element. In simple words, it has no relation to the number of electrons present in an atom. It only depends on the number of atoms present in a molecule.