BAND THEORY OF SOLIDS

BAND THEORY OF SOLIDS A solid contains an enormous number of atoms packed closely together. The energies of electrons within one isolated atom obey the following condition. 1) there are specific electronic energy levels around each atom. Electrons cannot occupy spaces between these levels. 2) electrons fill the lowest energy levels first. A specific quality of energy, called a quantum of energy, must be supplied to move an electron to the next higher level. 3)not more than two electrons may occupy the same energy level. Two electrons may occupy the same energy level because they have opposite magnetic characteristics. Atomic energy level is split up into a large number of closely spaced energy levels. A set of such closely spaced energy levels is called a energy band. In an energy band, the allowed energies are almost continuous. These energy bands are separated by regions, which have no allowed energy levels. These regions are known as forbidden bands or energy gaps. Based of Band Theory Solids are classified as conductors, insulators and semiconductors.