Classify metals, semiconductors and insulators on the basis of energy bands.

Explanation

(a) metals, (b) insulators and (c) semiconductors each Two distinguishing features : (i) In conductors, the valence band and conduction band tend to overlap (or nearly overlap) while in insulators they are seperated by a large energy gap and in semiconductors they are separated by a small energy gap. (ii) The conduction band, of a conductor, has large number of electrons available for electrical conduction. However the conduction band of insulators is almost empty while that of the semiconductor has only a (very) small number of such electrons available for electrical conduction.