This article describes the difference between the valence band and the conduction band. The valance band and conduction band represent the energy levels of the subatomic particles. In atomic structures, there exist an energy gap between the valance band and conduction band , and both energy bands are separated by a certain amount of energy.
The energy gap depends on the type of material. The energy gap is different for conductors, insulators and semiconductors. The energy gap between conduction and valance band indicates the electrical conductivity of the material. The less energy gap between the bands shows material is more conductive.
For example, in metals, both bands are almost touching each other. In insulators, there exist a wide energy gap between the valance and conduction band. In semiconductors, these bands are separated by a moderate amount of energy.
Thus, the atom of any material has two energy levels. The two energy levels are known as the valance band and conduction band. The conductivity of the material depends on the difference between the two energy levels.
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 an atom is excited by supplying energy. The valance band electrons act as free electrons when an 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 the 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 the valance band to the conduction band.
If the valance band and the conduction band overlap, as in the case of metals, very less energy is required to excite the valance band electrons to jump into the conduction band. Such types 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 a large forbidden gap and therefore the electric current does not flow even at high voltage.
Definition of Conduction Band
A conduction band is a band that has free electrons and is mainly responsible for conduction. When an atom is excited, the valance band electrons jump into the conduction band and now these electrons are free electrons and create an 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 the conduction band. When the atom is excited, the electrons cross the fermi level and reach the conduction band. The 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 exists below the fermi level, whereas the conduction band exists above the fermi level in the energy band diagram.
- When electrons in the valance band are excited by providing energy, the valance band electrons jump 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 are densely populated. Thus, the electron density in the valance band is more than the electron density in the 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 a higher energy level.
Major Difference between Valance Band and Conduction Band
Both the valance band and conduction band show the energy levels of the electrons. The difference between the conduction band and the valance band is shown in the following table.
| Basis of Difference | Valance Band | Conduction Band |
|---|---|---|
| Definition | The energy band that has the valance electrons of an atom is called the valance band. | The energy band that has free electrons in an atom is called the conduction band. |
| Abbreviation | Abbreviated as VB. | Abbreviated as CB. |
| Location in the energy band diagram | Below fermi level in the energy band diagram. | Above the fermi level in the energy band diagram. |
| Electrons are known as | The electrons present in the valance band are known as valance electrons. | The conduction band’s electrons are known as conduction electrons or free electrons. |
| Energy of electrons | The electrons in the valance band have less energy than the free electrons and fermi energy. | The electrons in the conduction band have more energy than valance electrons energy and fermi energy. |
| Effect of external energy | On application of external energy, electrons move from the valance band. | On application of external energy, electrons move from the valance band to the conduction band. |
| Nuclear forces | The valance band electrons are tightly bound to the nucleus. And, therefore the strong nuclear forces act on the valance band. | The conduction band electrons are loosely bound to the nucleus. And, therefore weak nuclear forces act on the conduction band. |
| Energy level | Electrons have lower energy levels in the valance band | Electrons have higher energy levels in the conduction band. |
| Band filling | Completely or partially filled with electrons. | Empty or partially filled with electrons. |
| Electron density | In the valance band, there are more electrons in a given space. Therefore, the electron density of the valance band is higher. | In the conduction band, there is less number of electrons in a given space. Therefore, the electron density of the conduction band is lower. |