→ A molecule is in general a group of two or more atoms that are chemically bonded together.

→ A molecule is the smallest particle of matter (except element) which is capable of an independent existence and show all properties of that substance.

→ Examples: ‘H2O’ is the smallest particle of water which shows all the properties of water.

→ A molecule may have atom of same or different elements, depending upon this, molecule can be categorized into two categories:

(i) Homoatomic molecules (containing atom of same element)

Examples: H2, O2, O3 , S8 , P4 etc.

(ii) Heteroatomic molecules or compounds (containing atoms of different elements)

Examples: H2O, CO2 , NaCl, CaCO3 etc.