The free electron theory of metals was first proposed by Drude and later improved by Lorentz. The main postulates of this theory are
1. All metal contain, adequate number of valence electron forming an electron gas which is free to move throughout the volume of the metal. A metal can be regarded as an array of positive ions permeated by a gas of free electrons.
2. The electron velocities in metals obey the classical Maxwell-Boltzmann distribution of velocities.
3. In the absence of an electric field the electrons move in random directions, making collisions from time to time with positive ions. Which are fixed in lattice.
4. The free electrons in the electron gas wander freely in the metal without any mutual interation. 6. When an electric field is applied to the free electrons are accelerated. They move in opposite direction to the electric field while maintaining their random motion.