Online Class 12 Chemistry Notes- Unit 1- Band Theory of Solids

Band Theory of Solids: A quantum mechanical model of electrons in solids that predicts certain restricted ranges or the bands, for the energies of these electrons is called as Band Theory of Solids. It is also called as energy band theory of solids. The behavior of an electron in a solid (and hence its energy) is related to the behavior of all other particles around it. This is in direct contrast to the behavior of an electron in free space where it may have any specified energy. The ranges of allowed energies of electrons in a solid are called allowed bands. Certain ranges of energies between two such allowed bands are called forbidden bands—i.e., electrons within the solid may not possess these energies. The band theory accounts for many of the electrical and thermal properties of solids and forms the basis of the technology of solid-state electronics.

A useful way to visualize the difference between conductors, insulators and semiconductors is to plot the available energies for electrons in the materials. Instead of having discrete energies as in the case of free atoms, the available energy states form bands.

Important energy bands in solids

There is a number of energy bands in solids but three of them are very important. These three energy bands are important to understand the behavior of solids. These energy bands are

Valence band
Conduction band
Forbidden band or forbidden gap

Read complete chapter click Class 12 Chemistry Notes- Unit 1- Band Theory of Solids

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