B. E. Douglas, D. H. McDaniel, J. J. Alexander, Concepts and Models of Inorganic Chemistry, 3rd edition, John Wiley & Sons, New York, 1994, page 305.
 
 

Problem 6.14

Sketch the curves for the distribution of energy states and their electron populations for a metallic conductor, and insulator, and a semiconductor.
 
 

Answer:

Metals have partially filled bands, insulators have filled valence bands and empty conduction bands with a large band gap, and semiconductors have partially filled valence and conduction bands due to thermal excitation across a small band gap.