♦ Learn about : Energy band , Types Of Energy Bands , conduction band , Unoccupied Band ,Valence Band , Forbidden Band ♦
(1) In an atom, electrons revolve round the nucleus in almost circular orbits of different radii representing shells and subshells.
Energy of electron in each subshell is definite.
These definite energy values are called energy levels of the atom.The energy levels (values) of electrons in outer shells are influenced by the presence of nuclei of other atoms.
Due to interatomic interaction, an energy E becomes E ± ΔE with different energy values within a small range on either side of E.
Thus each energy level line becomes broad (width = 2ΔE ).
This broadened energy level (line) is called energy band
Different Types Of Energy Bands :
(1) Conduction Band (C). The top most partially filled band, is called conduction band. It is so called because by accommodating more electrons in itself, the band provides mobility to electrons and helps in conduction.
(2)Unoccupied Band (U). The top most completely empty band is called unoccupied band. It represents a band of unoccupied energy levels which contain no electrons. When some electrons reach it after gaining thermal energy, it behaves as a conduction band.
(3)Valence Band (V). The upper most completely filled band, is called valence band.
(4) Forbidden Band (F). The band separating a balance band and an unoccupied (or a conduction) band, is called Forbidden band. The difference in the extreme energy levels of the forbidden band, is called energy gap (Eg)