Explain the classification of materials.

Explanation

Insulators: The valence band and the conduction band are separated by a large energy gap. The forbidden energy gap is approximately 6 eV in insulators. The gap is very large that electrons from valence band cannot move into conduction band even on the application of strong external electric field or the increase in temperature. Therefore, the electrical conduction is not possible as the free electrons are almost nil and hence these materials are called insulators. Its resistivity is in the range of 1011 - 1019m
Metals: In metals, the valence band and conduction band overlap. Hence, electrons can move freely into the conduction band which results in a large number of free electrons in the conduction band. Therefore, conduction becomes possible even at low temperatures. The application of electric field provides sufficient energy to the electrons to drift in a particular direction to constitute a current. For metals, the resistivity value lies between `10^(-2)` and `10^(-8)Omegam`.
Semiconductors: In semiconductors, there exists a row forhidden energy wap `(E_g lt3 eV)` between the valence band and the conduction hau t finite temperature thermal agitations in the solid can break the covalent bond between the stoms covalent bond is formed due to the sharing of electrons to attain stable electronic curation This releases some electrons from valence band to conduction band. Since free electrons are small in number, the conductivity of the semiconductors is not as high as that of the conductors The resistivity value of semiconductors is from `10^(-5)` to `10^(6)Omegam`.