ENERGY LEVELS
The energy levels, measured in electron volts (e.v.) in which orbiting electrons exist comply with a law of physics which states that energy can be given to electrons only in discrete amounts (quanta) which means that there are energy values that an electron cannot acquire. From this it can be deducted that there is a forbidden energy gap between each of the allowed energy bands K to O.
The width of the forbidden energy gap between the top of the valence band and the bottom of the conduction band determine the electrical conducting properties of materials.