On the basis of chemical constitution, all the matter can be classified into three groups:

(i) Elements- An element is a substance which cannot be split up into two or more simpler substances by the usual chemical methods of applying heat, light or electric energy. Sodium and Hydrogen are two elements.

(ii) Compounds- A compound is a substance made up of two or more elements chemically combined in a fixed proportion by weight. Water and sodium chloride are two compounds.

(iii) Mixtures- A mixture is a substance which consists of two or more elements or compounds not chemically combined together. Air and Gun powder are two mixtures.