What Is Energy Band Theory?
Electrons of an isolated atom are bound to the nucleus, and can only have distinct energy levels. How ever, when a large number of atoms, say, are brought close to one another to form a solid, each energy level of the isolated atom splits into N sub-levels, called states, under the action of the forces exerted by other atoms in the solid. These permissible energy states are discrete but so closely spaced that they appear to form a continuous energy band. In between two consecutive permissible energy bands, there is arrange of energy states which cannot be occupied by electrons. These are called forbidden energy states, and its range is termed as forbidden energy gap. The electrons in the outermost shell of an atom are called valence electrons and the energy band occupying these electrons is known as valence band. It is obviously the highest occupied band. It may be either completely filled or partially filled with electrons and can never be empty. The band above the valence band is cal
