1.22 In terms of band theory, what is the difference
(i) between a conductor and an insulator
Conductor: A conductor may conduct electricity through the movement of electrons or ions. The conductivity of metals depends upon the number of valence electrons available per atom. The atomic orbitals of metal atoms form molecular orbitals which are so close in energy to each other as to form a band. If this band is partially filled or it overlaps with a higher energy unoccupied conduction band, then electrons can flow easily under an applied electric field and the metal shows conductivity.
Insulator: If the gap between the filled valence band and the next higher unoccupied band is large then electrons cannot jump to it and such a substance behaves as an insulator.