Explain conductor (metal),insulator,and semiconductor by drawing diagrams based on energy bands.

(N/A) The difference between the minimum energy level of the conduction band $(E_c)$ and the maximum energy level of the valence band $(E_v)$ is called the energy band gap $(E_g)$.
There are no allowed energy levels in the region with the energy gap,hence this region is called the forbidden energy gap.
Depending on the type of material,the forbidden gap may be small,large,or zero. Based on this gap,materials are classified into three types:
$1$. Metal (Conductor):
As shown in figure $(a)$,a metal exists either when the conduction band is partially filled and the valence band is partially empty,or when the conduction and valence bands overlap. When there is an overlap,electrons from the valence band can easily move into the conduction band. When the valence band is partially empty,electrons can move to higher energy levels,making conduction possible. Therefore,the resistance of such materials is low and conductivity is high.
$2$. Insulator:
As shown in figure $(b)$,for an insulator,the energy gap $(E_g)$ is very large $(E_g > 3 \text{ eV})$. There are no electrons in the conduction band,and therefore,no electrical conduction is possible at room temperature.
$3$. Semiconductor:
For a semiconductor,the energy gap is small (typically $E_g < 3 \text{ eV}$). At room temperature,some electrons from the valence band can gain enough thermal energy to cross the small energy gap and enter the conduction band,allowing for limited electrical conduction.