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Difference between Valance Band and Conduction Band
In atomic structure, valance band and conduction band are the terms used to represent the energy levels of the subatomic particles, usually electrons. While analyzing the atomic structures, we found that the valance band and conduction band are separated by a certain amount of energy depending on the type of material.
For example, in metals, these are touching each other; in semi-conductors, these are separated by a moderate amount of energy; and in case of insulators, this separation is very large.
The energy gap between the valance band and the conduction band is known as forbidden energy gap. The diagram which is used to represent the conduction band, valance band and the forbidden energy gap graphically is known energy band diagram.
In this article, we will discuss the major differences between valance band and conduction band. Let's start with some basics first so that it becomes easier to understand the differences.
What is Valance Band?
The valance band is the energy band or energy level which comprises the valance electrons of an atom. Where, the valance electrons are the electrons in the outermost shell of the atom. The valance band is abbreviated as VB.
In the energy band diagram, the valance band is usually located at a lower energy level (i.e. bottom side of the diagram) with respect to the conduction band. The valance band is filled with valance electrons that have low energy. We may supply energy to the electrons of valance band by applying an external electric potential. After getting energy, the valance electrons jump into the conduction band and become conduction electrons. Generally, the electrons are always present in the valance band, therefore, it is either completely or partially filled with the electrons.
What is Conduction Band?
The conduction band is the energy band or energy level which comprises the free electrons. Where, the free electrons are those valance electrons which are free to move in the atomic structure and are responsible for the conduction of electricity and heat.
The conduction band is named so because it is entirely responsible for conduction of electricity in the materials. Basically, the conduction band contains those valance electrons that are excited to higher energy levels by the external potential in the valance band.
The conduction band is located at the higher energy level (or above the forbidden energy gap) in the energy band diagram. The conduction band is abbreviated as CB. The electrons of the conduction band are called free electrons or conduction electrons because they can move freely to conduct the electricity. Since, the conduction band electrons are required to have energy greater than fermi energy, therefore, the conduction band may be either empty or partially filled.
Difference between Valance Band and Conduction Band
Both valance band and conduction band are the energy levels of the electrons. However, there are several differences between them that are highlighted in the following table −
| Basis of Difference | Valance Band | Conduction Band |
|---|---|---|
| Definition | The energy band which comprises the valance electrons of an atom is known as valance band. | The energy band which comprises the conduction or free electrons of an atom is known as conduction band. |
| Abbreviation | The valance band is abbreviated as VB. | The conduction band is abbreviated as CB. |
| Location in energy band diagram | The valance band located below the fermi level (forbidden energy gap) in the energy band diagram. | The conduction band is located above the fermi level in the energy band diagram. |
| Electrons are known as | The electrons in the valance band are known as valance electrons. | The electrons in the conduction band are known as conduction or free electrons. |
| Energy of electrons | The energy of the valance band electrons is less than that of the free electrons and fermi energy. | The conduction band electrons have energy greater than fermi energy and energy of valance electrons. |
| Effect of external energy | Electrons leave the valance band when external energy is supplied to them. | Electrons reaches the conduction band when they are supplied with external energy. |
| Nuclear forces | The strong nuclear forces act on the valance band, i.e. the valance band electrons are strongly bound to the nucleus. | The weak nuclear forces act on the conduction band, which means the conduction band electrons are weakly bound to the nucleus. |
| Energy level | The valance band is a lower energy level of the electrons. | The conduction band is a higher energy level of the electrons. |
| Band filling | The valance band is either completely or partially filled with the electrons. | The conduction band is either empty or partially filled with the electrons. |
| Electron density | The electron density of valance band is high because it has more electrons per unit volume. | The electron density of conduction band is low. |
Conclusion
The most significant difference that you should note here is that a Valance Band is the low energy state of electrons, while a Conduction Band is the high energy state of electrons.
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