Question

What is atomicity?

Answer 1

- Hint: Atomicity is the term that is associated with molecules. It is sometimes referred to as the valency.

Complete step-by-step solution -

Atomicity can be defined as the total number of atoms that is present in a molecule of an element. Molecules of different elements have a different number of atoms present in it. Atomicity of molecules can be classified into different groups:
(1). Monoatomic molecules: The molecules which are composed of 1 atom are known as monatomic molecules. For example, Neon (Ne), Helium (He), Argon (Ar), etc. All noble gases are monatomic.

(2). Diatomic molecules: The molecules which are composed of two atoms are known as diatomic molecules. The gases that are the main constituents of the atmosphere are diatomic. Nitrogen ($N_2$) which constitutes about 78% of the atmosphere and oxygen ($O_2$) which constitutes 21% of the atmosphere is diatomic.

(3). Triatomic molecules: The molecules which are composed of three atoms are called triatomic molecules. Ozone ($O_3$) is triatomic and it is a very important gas present in the stratosphere level of the atmosphere. The ozone layer protects the earth from the harmful Ultraviolet rays.

(4). Tetratomic molecules: The molecules which are composed of four atoms are known as tetratomic molecules. Tetra phosphorus ($P_4$) is a tetra atomic molecule. It is also known as white phosphorus or yellow phosphorus. The atoms in $P_4$ are arranged in a tetrahedral structure. White phosphorus, when exposed to light turns yellow and that’s the reason it is also called the yellow phosphorus.

(5). Polyatomic molecules: The molecules which are composed of more than four atoms are known as polyatomic molecules. For example, Octa-sulphur ($S_8$) is polyatomic and a molecule of octa-sulphur has 8 atoms of sulphur.

Note: Some elements like carbon do not have very simple structures. They may contain indefinite numbers of atoms that are bonded together to form a molecule of that element. In those cases, their atomicity cannot be calculated and is generally considered 1. Don’t confuse between them.