Electron Theory of Metals

In an ionic solid, the atom forming a cation gives up its valence electron that is captured by the atom forming an anion. Here the electrons are strictly localized. However in metals, the core electrons are localized at the atoms but the valence electrons are delocalized and belong to the entire solid. The behaviour and energy states of these delocalized electrons determine many properties of these solids. We shall try to understand the behavious of these electrons and see how they influence the property of the solid. The simplest approach is the classical free electron model that was successful in explaining some of the properties of metals. This was succeded by the more sophisticated band theory of solids. The general characteristics of electrical conductors are: (i) The current density in the steady state is proportional to the electric field strength (Ohm’s law). (ii) For pure specimens, the electrical conductivity (σ) and the thermal conductivity (k) vary with temperature as follows: σ ∝ T−1 and k = constant (for T > θD) so that σT