Question

Why do energy bands form in a polyatomic solid? Pick one and explain

A) some materials are metals and others insulators

B) electron energy levels split to satisfy the pauli exclusion principle.

C) empty electron orbitals overlap with filled orbitals.

D) ion cores need to vibrate at elevated temperatures.

E) none of the above

Answer 1

Electrons in atom occupy atomic orbitals of some discreet energies. But if two atoms combine together we get, their atomic orbitals combine to give two molecular orbitals and electrons now occupy molecular orbitlas. According to Pauli's principle two electrons can occupy one orbital. Like I have shown in the picture when large amount of atoms combine to form a molecular solid very large no. of orbitals are formed which are very closely spaced in terms of energy and they look like a continuous energy or band-like structures. Half of these band is filled with electrons and other half is empty ( in simple cases ), this further gives rise to valence band and conduction band concept which is not required to discuss here. I hope picture makes sense.