Energy Bands in Solids

Section 9.1 builds the energy-band picture of a solid from scratch: in an isolated atom the electron energy levels are widely separated and discrete, but when millions of atoms are packed together in a solid, the outermost orbitals of neighbouring atoms overlap and split into a near-continuum of closely spaced levels that looks like a continuous energy BAND. This band structure -- and specifically the size of the gap between the band electrons occupy at rest and the band they must reach to conduct -- is what …