Question

The highest occupied energy band is called _____________ and lowest unoccupied energy band is called the ___________________.
A) Band Gap, Conduction Band
B) Valance band, Band Gap
C) Conduction band, Valance band
D) Valance Band, Conduction Band

Answer 1

Hint:
An energy band is created by the stacking of a number of energy levels in a number of atoms forming a lattice. The lowest unoccupied band is the one which contains excited electrons of the atom.

Complete step by step solution:
An isolated atom possesses a number of discrete energy levels having distinct energies. When two atoms are brought into close proximity to each other, the electrons in the outer orbitals of the atoms interact with each other. Now if instead of two atoms, ‘N’ numbers of atoms are brought close to each other, then it gives rise to ‘N’ number of closely spaced orbitals instead of discrete energy levels. This is known as the band of allowed energy levels or the valence band. There is another band of energy levels which is formed from the energy levels that are unoccupied and have higher energy and can take up electrons when excited. These energy levels form the conduction band which take up the electrons when they are excited by higher energy radiation.
Hence, the highest occupied energy band is called the “valence band” and the lowest unoccupied energy band is called the “conduction band”.

Thus, the correct option is D.

Note:
There is a region between the bands of allowed energy levels called the forbidden region. This region is also called the bad gap region. In case of the insulators, there is no band gap or forbidden region in between the valence and the conduction band that is why they are good conductors of heat and electricity.