Draw the bands of MO energy levels and the electron population for: (a) A semiconductor (b) An electrical insulator Explain why a semiconductor has the higher electrical conductivity.

Band theory explains the electronic structure of solids, where energy levels are grouped into bands. The valence band is filled with electrons, while the conduction band is typically empty. The energy gap between these bands determines the electrical properties of materials: conductors have overlapping bands, semiconductors have a small gap, and insulators have a large gap.

Electrical conductivity refers to a material's ability to conduct electric current. In semiconductors, the small energy gap allows electrons to be thermally excited from the valence band to the conduction band, enabling current flow. In contrast, insulators have a larger gap, making it difficult for electrons to move, resulting in low conductivity.

Doping is the intentional introduction of impurities into a semiconductor to modify its electrical properties. By adding donor or acceptor atoms, the number of charge carriers (electrons or holes) can be increased, enhancing conductivity. This process is crucial for creating p-type and n-type semiconductors, which are essential for electronic devices.