O u t l i n e
As we came to understand from Chapter 2, when atoms are brought together in crystals, their outermost electrons are influenced by a periodic potential. Therefore, the possible electron energies form bands of allowed values separated by bands of forbidden values. This band structure is of fundamental importance in explaining the properties of metals, semiconductors, and insulators. The most accepted and most accurate theory in modern physics today, to predict physical, mechanical, chemical, and electrical properties of atoms, molecules, and solidsincluding the band theory of solids-is quantum mechanics.