The force of attraction or repulsion acting between the molecules are known as intermolecular force. The nature of intermolecular force is electromagnetic.

The intermolecular forces of attraction may be classified into two types.

Cohesive force

Adhesive force

The force of attraction between molecules of same substance is called the force of cohesion. This force is lesser in liquids and least in gases.

The force of attraction between the molecules of the different substances is called the force of adhesion.

 

Ex. (i) Two drops of a liquid coalesce into one when brought in mutual contact.

(ii) It is difficult to separate two sticky plates of glass welded with water.

(iii) It is difficult to break a drop of mercury into small droplets because of large cohesive force between the mercury molecules.

Ex. (i) Adhesive force enables us to write on the blackboard with a chalk.

(ii) A piece of paper sticks to another due to large force of adhesion between the paper and gum molecules.

(iii) Water wets the glass surface due to force of adhesion.

 

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