Kamins pg:4, When the atomic spacing equals the crystal-lattice spacing

(because of spin degeneracy). In Figure l.Ib the splitting of two discrete allowed energy
levels of isolated atoms is indicated in a sketch that shows what the allowed energy levels
would be if the interatomic distances for a large assemblage of atoms could be varied con-
tinuously. Under such conditions, the discrete energies that characterize isolated atoms split
into multiple levels as the atomic spacing decreases. When the atomic spacing equals the
crystal-lattice spacing (indicated in Figure l.Ib), regions of allowed energy levels are typ-
ically separated by a forbidden energy gap in which electrons cannot exist. An analogue
to atomic energy-level splitting exists in mechanical and electrical oscillating systems
which have discrete resonant frequencies when they are isolated, but multiple resonance

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