An element is simplest pure substances that can neither be divided into simpler ones nor can it be made from two or more substances by any method e.g: hydrogen, helium and etc.

A compound is a substance formed by the combination of two or more than two elements.

An atom is the smallest particle of an element which can take part in the chemical reaction.

The smallest particles of an element or a compound is called molecule.

Any two examples of compounds are sodium chloride and sodium oxide.