MOLECULES AND SOLIDS!

Molecules show “bands” instead of energy levels. This is because there are so many more quantum degrees of freedom that a molecule displays, the quantum equivalent of classical rotations and vibrations, plus the many ways electron state functions in neighboring atoms can overlap.


In solids, the number of different ways electron state functions in neighboring atoms can overlap becomes almost limitless, so the energy levels for electrons merge into broad bands that are practically continuous since they contain billions and billions of closely spaced different energy levels!

The basis of all modern electronics... “doped” semiconductors forming a diode... a switch with no moving parts, as small as you please.