Explain insulator in terms of energy bands?

In terms of energy bands, an insulator is a material that has a large energy gap between its valence band and conduction band. This energy gap is typically too large for electrons to easily move from the valence band to the conduction band, making it difficult for the material to conduct electricity.

In an insulator, the valence band is fully occupied with electrons, while the conduction band is empty or only partially filled. This large energy gap prevents electrons from gaining enough energy to move into the conduction band and flow freely through the material.

As a result, insulators have very high resistivity and do not conduct electricity well. Examples of insulators include glass, rubber, and plastic.