Types of Material--

On the basis of their electrical conductivity materials are devided into two categories:

(i). Conductors— The materials which have one, two or three electrons in their outer most shell have the tendency to loose these electrons. So, these electrons move randomly in the entire material, called Free Electron. When we apply a voltage source across the material these electrons start moving from negative terminal to positive terminal and start conduction of electricity. Hence these materials are called Conductors. e.g. metal like silver, copper, iron, acids, alkalies etc.

(ii). Insulators—The materials which have five, six, seven or eight electrons in their outer most shell do not allow to go away through them. So, these electrons are called Bound Charge. Hence, they do not conduct electricity through the material, these materials are called Insulators. e.g. glass, wood, wax, mica etc.