Metal Band Theory


The molecular orbitals that help in the formation of the band seem to have the same energy as the atomic orbitals. This theory mainly describes the fact that electrons can jump from the valence band to the conduction band. This process happens when the temperature remains ordinary because it can help the solids to conduct electricity. The conductivity mainly depends upon the gap between the valence band and conduction band.

Description of Metal Band Theory

Band theory is considered a concept that focuses on the matter of solids. This theory is also known as zone theory and it shows the relationship between valence and conduction bands. In this part, the valence band describes the orbitals of the valence shell and they contain electrons.

On the other hand, the conduction band is formed of orbitals. Therefore, it can be said that the orbitals of the conduction band are empty. The development of this theory occurs by gathering the knowledge that is witnessed during the quantum revolution in science. As per the view of this theory, atomic orbitals are an important part of the electron particles. It helps to give a shape to the distinct arrangement of the energy levels.

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Figure 1: Energy Bands for Solids

The theory shows that solids electrons jump from valence band to conduction band. This happens when the temperature stays ordinary and in this state solid conducts electricity. This matter of conductivity mainly depends on the gap between the valence band and conduction band. The most important factor here is that when the gap between these bands is equal to or more than 5ev then the material will behave as an insulator.

It also exposes the fact that when the energy different lies equal to or less than 3ev, then the material is named as semiconductor. In contrast, the overlapping of the valance and conduction band is called conductors. The reason behind this factor is that electrons can jump from valance to conduction band and thus conduct electricity. The semiconductors are the factor where few electrons can jump from valance band to conduction band.

Valence Band, Conduction Band, and Forbidden Gap

The Band Theory of Metals is dependent upon the valance band and conduction band. This theory is also known as the band theory of solids or zone theory of solids. The matter defines the aspects of conductor, semiconductor, and insulator very clearly. The description of the terms is given below-

Valence Band: This band is built up of the specific valence shell orbitals and it consists of electrons in them. An example of this factor is that a sodium valence band is made up of 3s1 orbital. It consists of the configuration of the electron of sodium and it is 1s2, 2s2, 2p6, 3s1.

Conduction Band: the band of conduction is built up of orbitals which are unoccupied by electrons. They are seen either in the valence shell or in the higher unoccupied shell. That is the reason to develop the conduction band empty. This factor describes that the highest energy band is known as valance band.

Forbidden Gap: Forbidden Gap is an important part of the band structure of sodium. In this part, this gap is considered the energy difference between the valance band and conduction band.

The matter regarding this theory also describes some other points such as conductors, semiconductors, and insulators. Conductors are the materials which allow electricity to pass through them. Some examples of this factor are zinc, iron, copper and many more.

Semiconductors are the materials which show the conductivity between conductors and insulators. Some factors can be given as examples and they are As, Ge, and Si. Insulator is defined as the materials that hinder electricity to pass through them.

Examples of the insulators are stones, grass, wood and many more.

Examples of Band Theory

The explanation of band theory can be defined with the example of sodium and it will help to understand the matter very easily. The atomic configuration of sodium is1s2, 2s2, 2p6, 3s1. It consists of unpaired electron in the 3s orbital and they overlap with each other.

The process has happened for the formation of molecular orbitals. The energy difference presents the energy spread between the bonding orbital and anti-bonding orbital. The highest gap between the valence band and the conduction band hinders electrons to jump from one band to another. This incident is noted as less or no conductivity.


The tutorial describes that metal band theory is based on the valence band and conduction band. They are the main aspects of this theory and that is the reason this theory is also called the theory of solids or zone theory. The theory gives the description of different aspects which are important for this factor. The aspects are conductors, insulators, and semiconductors. Other important factors of this theory include the forbidden gap, valance band, and conduction band.


Q1. Who gives the proposal of the metallic band theory?

Ans. The revolution of quantum helps in the development of metal band theory. It is seen that in the year 1928, Felix Bloch applies the idea of quantum theory. Later, in 1927, Walter Heitler and Fritz London discovers the idea of this theory.

Q2. What is the reason for the formation of the band gap?

Ans. The gap is formed when two bands are not wide enough to span the full range of electron energy levels. The band gap is the gap between the valance band and conduction band.

Q3. What is the benefit of band theory?

Ans.Band theory helps to know the difference between conductor, semiconductor, and insulator. The difference is made by plotting available energies for an electron in a material.