Question

What is the atomicity of HCl?

Answer 1

A molecule is the basic building block of a substance that can normally exist on its own. When two or molecules of the same type combine to form an element. There are two laws of chemical combination established about element combination and formation of a molecule are the law of conservation of mass and the law of constant proportions.

Complete step by step answer:
According to the law of conservation of mass states that mass can neither be created nor destroyed in a chemical reaction by molecules.
The law of constant proportions states that in a chemical substance the elements are always present in different proportions by mass.
The same type atoms from elements combine to form a molecule, such as Argon (Ar), Helium, etc. like molecules made up of one element. But in the case of non-metals, for example, an oxygen molecule will form by the combination of two atoms which is known as a diatomic molecule.
Hence, the number of atoms combined to form a molecule is known as that molecule atomicity.
Atomicity of some non-metal elements given in the below table:

Name of the molecule	Formula	Atomicity
Argon	Ar	Monoatomic
Helium	He	Monoatomic
Oxygen	${{O}_{2}}$	Diatomic
Hydrogen	${{H}_{2}}$	Diatomic
Ozone	${{O}_{3}}$	Triatomic
Sulfur	$S({{S}_{8}})$	Poly-atomic

Given a molecule, HCl, i.e, hydrochloric acid is made up of two atoms. 1 atom is an H atom and another atom is Cl. So, the atomicity of HCl = 2. Hence HCl is a diatomic molecule.

Note: When two or more atoms of elements combine to form a molecule of a compound. For example, water, ammonia, carbon dioxide, methane, etc. metals and some other elements like carbon, do not have a simple structure but form a very large number of atoms bonded together.