Updated: Mar 2
The atom of any material has two energy levels. The conductivity of the material depends on the difference between two energy levels. The two energy levels are known is valance band and conduction band.
Definition of Valence Band
The valance band of any specific material is the outermost electron orbital of any atom. The electrons in the valance band can jump to the conduction band when atom is excited by supplying energy. The valance band electrons acts as a free electrons when atom is excited.
The energy difference between the highest occupied energy of the valence band and the lowest occupied energy of the conduction band is known as band gap or forbidden energy gap.The band gap indicates the conductive property of the material. The large band gap indicates that a lot of energy is required to excite the valance band electrons in order to throw out the electrons from valance band to conduction band.
If the valance band and the conduction band overlaps, as in case of metals, very less energy is required to excite the valance band electrons to jump into conduction band.Such type of materials have very high conductivity.
The band energy or forbidden energy gap is sometimes abbreviated as VB. The energy gap depends on the type of material. The forbidden energy gap of metal, semiconductor and insulator are different.
The insulators have large forbidden gap and therefor the electric current does not flow even at high voltage.
Definition of Conduction Band
A conduction band is the band that have free electrons and are mainly responsible for conduction. When atom is excited, the valance band electrons jump into the conduction band and now these electrons are free electrons and creates electric current. The conduction band is abbreviated as CB.
The valance band electrons may reach up to the fermi level. The fermi level is the electron energy level at zero degree centigrade. The fermi level lies in between the valance band and conduction band. When the atom is excited, the electrons crosses the fermi level and reach in the conduction. Forbidden energy gap or band gap of conductor, semiconductor and insulating materials is as given below.
Key Differences Between Valence Band and Conduction Band
The valance band exist below the fermi level,whereas the conduction band exist above the fermi level in the energy band diagram.
When electrons present is the valnce electrons are excited by providing energy, the valance band electrons jumps into the conduction band.
The valence band is partially or completely filled, whereas the conduction band is empty or partially filled at room temperature.
The electrons in the valance band is densely populated. Thus, the electron density in the valance band is more than the electron density in conduction band.
The nucleus exerts more force on the electrons present in the valance band.The nucleus exerts less force on the electrons present in the conduction band.
The valance band is a lower energy state. The conduction band is at higher energy level.