Question

In terms of bond theory, explain the difference between a conductor (metal),
semiconductor and insulator. Give examples.

Answer 1

Hint: As we know that the atomic orbitals of the metal atoms form molecular orbitals which together form a band and outermost filled energy band is the valence band and next empty band in which electrons can move is conduction band.

Complete Step by step answer:
As we know that according to band theory the atomic orbitals of the metal atoms form molecular orbitals which together form a band as they are very close in energies with each other and the outermost filled energy band is called the valence band and the next empty band in which electrons can move is called the conduction band.

Now in metals, the conduction band is very close to the valence band and when electric current is applied the electrons can easily move from conduction band to valence band and therefore metals will behave as conductors. Also the partially filled valence band will behave as a conductor. For example Lithium.

If the gap between the valence band and the conduction band is very large, the electrons will not be able to jump from conduction band to valence under applied electric current and thus will not be able to produce electricity and the metal will behave as an insulator. Also the fully filled valence band will behave as an insulator.

In case of semiconductors, there is only a small energy gap between the valence band and the conductance band therefore some of the electrons can jump to the conduction band by acquiring extra energy and thus they will show some conductance and are called semiconductors. For example Silicon and Germanium.

Note: Semiconductors are also called intrinsic semiconductors as on heating the electrons can jump from valence band to the conductance band. Their conductivity is very low which can be increased by adding appropriate amounts of suitable impurities to Silicon and Germanium and this addition is called doping which helps them to be converted to semiconductors.