Electron theory of metals

The most characteristics properties of metals are their high electrical and thermal conductivities.

For eg. :-The electrical conductivity at room temperature of silver is 0.6 X 10⁸ ohm^-1m^-1 as compare to  10^-16 for a good insulator and 2 X 10^-2 for a semiconductor such as germanium.

            The idea that the large electrical and thermal conductivity of metals might be explaind by the presence of mobile electrons (also called “free” or “conduction” electrons) in the metals was first put forward by Drude well before the introduction of quantum theory.

             Lorentz and Drude considered that about 95% of whole volume of solid is occupied by the electrons and 5% of the volume is occupied by ion core.hence according to free electron theory,the solids behaves as free electron gas.

 

Electron theory of metals

The electron theory of metals was developed by Drude & Lorentz , so it is also known as Drude-Lorentz theory of metals.This theory says that "A metal crystal consists of positive metal ions whose valence electrons are free to move between the ions as if they equvalent to an electron gas.The crystal is then imagined to be held together by electrostatic forces of attractions between the positvely charged ions and negatively charged electron gas.It is than assumed that the electrons are free to move in every part of the entire crystal"
         The mutual repulsion between negative electrons is ignored to this theory and the potential field due to the positive is assumed to be completely uniform.
         The free electrons in a metal move iso-tropically and move in a particular direction on an application of electric field.Because of elastic collisions,the magnitudes of steady-state current is proportional to the voltage applied provided the temperature of metals remains constant.