Conductors and Semi-Conductors

Materials can be classified into three groups according to their electrical properties.The number density of free electrons is the number of electrons per unit volume of material. The three groups of materials are:Conductors. These have a very high number density in the order about 10²⁸m^-3
Semi-conductors. These have a lower number density of about 10¹⁷m^-3. An increase in temperature releases more free electrons.With semi-Conductors, the number of charge carriers increases with temperatureso the resistance decreases with temperature.Pure semiconductors are called intrinsic semiconductors.Conduction is due to the electrons that break free.
Insulators. These have a very low number density.No electrons move through the insulator.The electrons are attached to the atoms.