Write a short note on Valence band.

Hint:According to the band theory in solid state physics, there are two types of bands namely the valence and the conduction band which describes the nature of solids. The movement of the charge carriers from band to another requires energy as shown in the figure below.

Complete step-by-step solution:
The band theory is an interesting topic which explains why certain objects conduct electricity while others don’t. According to this theory, the valence band contains the valence electrons which have less energy as compared to that of the conduction bands. The conduction band is mostly empty or partially filled with electrons. The difference in energy between the two bands results in the distinguishing of the metal into conductor, semi-conductor and insulator.
Consider the image shown below, if the two bands overlap then the given metal is said to be a semiconductor. If there is a small energy difference between the two bands, it's called the semiconductor. The energy difference in a semiconductor is also called the Fermi-energy level. If there is a huge difference between the two energy levels it is called the insulator.

Thus, we can conclude that the valence band is filled with valence electrons, which needs energy to get excited to the conduction band. The valence band has less energy as compared to both the Fermi level and the conduction band.

Note: The metal conducts electricity only if it is present in the conduction band. Electrons need energy to move from the valence band to the conduction band, this is called the excitation of electrons. The energy difference in a semiconductor is also called the Fermi-energy level.