Question #0f860
1 Answer
The band gap between the valence band and the conductance band in terms of the molecular orbital of the compound is too large for electronic excitation to the conductance band.
Explanation:
In a conductor the conductance band, which is made up of molecular orbitals from molecular orbital theory (MOT), is empty but overlaps with the valence band which is also made up of molecular orbitals but contain the outer electrons of the atoms, hence it is called the valence band. When energy is applied in terms of current (energy) the outer electrons jump to (get excited to) the conductance band thus producing a flow of current (electricity).
However with insulators the band gap between the empty conductance band and valence band is too large for electrons to cross over when energy is applied, thus no flow of electricity occurs.
Image from: http://www.globalspec.com/reference/13668/160210/chapter-9-2-semiconductor-basics
More info about Valence and Conduction Bands here: https://en.wikipedia.org/wiki/Valence_and_conduction_bands
Hope I helped :)
