Final answer:
Metals, semiconductors, and insulators can be distinguished based on the size of the band gap between the valence band and the conduction band. Conductors have a small band gap and can easily conduct electricity, while insulators have a large band gap and are poor conductors. Semiconductors have a moderate band gap and can conduct electricity better than insulators, but not as well as conductors.
Step-by-step explanation:
In terms of electronic energy band theory, metals, semiconductors, and insulators can be distinguished based on the size of the band gap between the valence band and the conduction band.
In a conductor, the highest energy band with electrons is partially filled, and the band gap is very small. This allows electrons to easily move from the valence band to the conduction band, making conductors good conductors of electricity.
In an insulator, the highest energy band with electrons is completely filled, and the band gap is large. As a result, very few electrons can move into the conduction band, making insulators poor conductors of electricity.
Semiconductors have a relatively small energy gap between the valence band and the conduction band. The band gap is moderate compared to conductors and insulators, allowing for some electrons to be thermally excited into the conduction band at room temperature. This makes semiconductors conduct electricity better than insulators, but not as well as conductors.