Question

The band gaps of an insulator, conductor, and semiconductor are respectively $E_{g_1}$​, $E_{g_2}$ and $E_{g_3}$​. The relationship between them is given as ____________.
A) $E_{g_1}$​>$E_{g_2}$​<$E_{g_3}$​
B) $E_{g_1}$​>$E_{g_2}$​>$E_{g_3}$​
C) $E_{g_1}$​<$E_{g_2}$​>$E_{g_3}$​
D) $E_{g_1}$​<$E_{g_2}$​<$E_{g_3}$​

Answer 1

Hint: A bandgap is defined as the distance between the valence band of electrons and the conduction band. It is useful for predicting the wavelength of light that will be absorbed by the material. Electron band gap helps in understanding the characteristics of metals, non-metals, and semiconductors. Electron band gap pertains to solid-state chemistry.

Complete solution:
There is no band gap in a conductor when the valence band and the conduction band in a conductor overlap each other. Also, Insulator has the largest band gap among insulator, conductor, and semiconductor.
Hence the increasing order of the band gap = Conductor < Semiconductor < Insulator
$ \Rightarrow $\[{E_{g2}} < {E_{g3}} < \;{E_{g1}}\]
 $ \Rightarrow $\[{E_{g1}} > {E_{g2}} < \;{E_{g3}}\]

Hence the correct option is A.

Note: 1) There are two types of electron bands, the Valence band, and Conduction band. The valence band is the space that is outermost in the electronic configuration of atoms. The conduction band is the space into which electrons from the valence band can be transferred upon excitation. The concept is also used in understanding the interaction of light with matter.
2) Conductor is an object that allows the flow of charge in or more directions. Electrons move freely within the conductor. The electric field exists on the surface but the field is zero inside. The resistivity of a conductor depends on temperature and the material.
 3) An insulator is a material in which the electrons do not flow freely. They do not permit heat and electricity to pass through it. The electric field does not exist.
4) Semiconductor is a crystal material which acts as a conductor sometimes and as an insulator sometimes.