Matter on the basis of chemical composition can be classified as follows :

i. Pure substances : 

They always have a definite chemical composition. They always have the same properties regardless of their origin. e.g. Pure metal, distilled water, etc.

They are of two types :

a. Elements : 

They are pure substances, which cannot be broken down into simpler substances by ordinary chemical changes. 

Elements are further classified into three types :

1. Metals :

• They have a lustre (a shiny appearance). 
• They conduct heat and electricity. 
• They can be drawn into wire (ductile). 
• They can be hammered into thin sheets (malleable). 
• e.g. Gold, silver, copper, iron. Mercury is a liquid metal at room temperature.

 2. Nonmetals :

• They have no lustre, (except diamond, iodine) 
• They are poor conductors of heat and electricity, (except graphite) 
• They cannot be hammered into sheets or drawn into wire, because they are brittle. e.g. Iodine

3. Metalloids : 

Some elements have properties that are intermediate between metals and nonmetals and are called metalloids or semimetals.

e.g. Arsenic, silicon and germanium.

b. Compounds : 

They are the pure substances which are made up of two or more elements in fixed proportion. 

e.g. Water, ammonia, methane, etc.

ii. Mixtures : 

They have no definite chemical composition and hence no definite properties. 

They can be separated by physical methods. e.g. Paint (mixture of oils, pigment, additive), concrete (a mixture of sand, cement, water), etc.

Mixtures are of two types :

• Homogeneous mixture : In homogeneous mixture, constituents remain uniformly mixed throughout its bulk. e.g. Solution, in which solute and solvent molecules are uniformly mixed throughout its bulk.
• Heterogeneous mixture : In heterogeneous mixture, constituents are not uniformly mixed throughout its bulk. e.g. Suspension, which contains insoluble solid in a liquid.