Question

In terms of band theory, what is the difference between a conductor and an insulator?

Answer 1

In an insulator, the energy gap between the fully occupied highest band and the conduction band (ΔE₀) is substantial, whereas in a conductor, the highest occupied band is either partially filled or overlaps with the conduction band if it is fully occupied.

Answer 2

	Conductor	Insulator
1.	The valence band and the conduction band overlap, or the valence band is partially filled.	There is a large energy gap (band gap) between the completely filled valence band and the empty conduction band.
2.	Electrons can easily move to higher energy states within the same band or to overlapping bands.	Electrons cannot easily jump across this large gap.
3.	This free movement of electrons enables high electrical conductivity.	As a result, electrical conductivity is extremely low or absent.