Band theory of Metals

Introduction to Band theory of metals

Do you know what is molecular orbital band theory? Metals carry electricity with the aid of valence electrons, according to the band theory of metals. The same-energy atomic orbitals of metals combine to produce molecular orbitals near energy to one another to form a band. Electrons can readily flow under an applied electric field if the band is partially filled or coincides with another higher energy uninhabited conduction band, resulting in high conductivity.

Describe the band theory

Even at normal temperature, electrons can hop from the valence band to the conduction band, according to solid-state band theory, and the solid conducts electricity as a result. Conductivity is determined by the distance between the valence and conduction bands. The material will function as an insulator if the spacing or energy difference between both the valence band and the conduction band is greater than or equal to 5ev.

A semiconductor is a substance or solid in which the difference in energy between the valence band and the conduction band is equivalent to or less than 3ev. When the valence band and the conduction band overlap, the solid is referred to as a conductor. It is based on the fact that electrons may jump from the valence band to the conduction band, allowing electricity to flow.

Electrons cannot move from the valence band to the conduction band if the gap between them is too large (more than or equal to 5ev). As a result, these materials or solids cannot conduct electricity. A few electrons may leap from the valence band to the conduction band if the valence and conduction bands are not overlapping or separated by a large distance; these materials are known as semiconductors.

What is the Band Theory of Metals

The band theory of metals is based on the valence band and the conduction band. It is also known as the band theory of solids or zone theory of solids. It defines conductors, semiconductors and insulators very clearly and distinctly. 

The quantum state that an electron acquires inside a metal solid is described by the band theory of solids. Every molecule has several different energy levels. The band theory explains how electrons behave inside a molecule quite effectively. The band theory arose from scientific information obtained during the quantum revolution. Felix Bloch applied quantum theory to solids in 1928.

Following are a few of the important terms associated with the band theory.

Valence Band

The valence band is the energy band that contains the energy levels of valence electrons. This band may be found beneath the conduction band. In addition, the electrons in this band are weakly connected to the nucleus of the atom. It’s made up of electron-filled valence shell orbitals. A sodium valence band, for example, is made up of 3s1 orbitals. 1s2, 2s2, 2p6, 3s1 is the electrical configuration of sodium.

A valence band exists beneath the conduction band. The energy of electrons in the valence band is lower than that of electrons in the conduction band.

Conduction Band

This energy band contains the energy level of unbound electrons. External energy must be applied in a way that the valence electrons push to the conduction band and become free for electrons to be free. It’s made up of orbitals in the valence shell and upper empty shell that aren’t occupied by electrons. As a result, the conduction band’s orbitals are vacant. Let’s use sodium as an example: following orbital 3s, the next orbital 3p is unoccupied, forming a conduction band.

The conduction band is normally empty. When external energy is supplied, electrons from the valence band jump into the conduction band, becoming free electrons. The energy of electrons in the conduction band is higher than that of electrons in the valence band.

Forbidden Band

We also refer to this as the forbidden gap. This is the energy gap that exists in the middle of the valence band and the conduction band. We determine the electrical conductivity of a solid from the forbidden gap. Additionally, we can also determine the classification of the materials as conductors, semiconductors and insulators.

Thus, in other words, we can say the highest energy band that is filled is known as the valence band. While the next available band in the energy structure, which is empty, is called the conduction band. 

Band Structure of Sodium

The band structure of sodium can be shown as follows :

• Forbidden Gap: The gap or energy difference between the valence band and the conduction band is called the forbidden gap. 
• Conductors: The materials which allow electricity to pass through them are called conductors. Examples: copper, iron, zinc, etc. 
• Semiconductors: The materials which show conductivity between conductors and insulators are called semiconductors. Examples: Si, Ge, As, etc. 
• Insulators: The materials which do not allow electricity to pass through them are called insulators. Examples: wood, glass, stones, etc.

Explain Band Theory of Metals

The redistribution of free electrons among a lattice of positively charged metal ions is represented by the band theory of metallic bonding. Metallic bonds have a different structure than covalent and ionic ones. They are responsible for the connection between metal atoms. Ionic bonds, on the other hand, connect metals to nonmetals, and covalent bonds connect nonmetals to nonmetals.

The valence electrons from the interacting metal atoms, s and p orbitals, are delocalised in metallic bonding. Instead of circling their individual metal atoms, the interacting metal ions form a “sea” of electrons that surrounds the positively charged atomic nuclei. The electrons are then free to travel around between the atomic nuclei.

Unique properties of Metals

A variety of distinctive qualities of metals are explained by the characteristics of metallic bonds:

• Since the electrons in the electron sea are free to travel and transport electric current, metals are good conductors of electricity.
• As the local connections may be quickly dissolved and repaired, metals are ductile and malleable.
• Metals are lustrous. Photons reflect off the metal surface since light cannot permeate it. The frequency of light at which photons are reflected, however, has an upper limit.
• Different elements can create metallic connections, resulting in an alloy. Metallic bonding is demonstrated with aluminium foil and copper wire.

Conclusion

Here the article covered the topic of band theory of metals, including different types of bands that the topic has. We also looked into the band structure of sodium, which can be an important part of exam preparations.