A Short Note on Band Theory Of Metals

Metals conduct electricity with the help of valence electrons, which are present in the metal. The atomic orbitals or electron cloud of metals have the same energy, which combines to form molecular orbitals whose energies are closer to one another, resulting in the formation of the ‘band’ of metals. Electrons can flow under the influence of an applied or exerted electric field with little effort if the band is partially filled or overlaps with another high energy-free (unoccupied C.B. i.e. conduction band). In this condition, the electrons can flow with little effort under the influence of an applied or exerted electric field, resulting in high conductivity. So, for example, sodium is used as an example in this section (Na).

Sodium’s atomic or electronic configuration is “1s², 2s², 2p⁶, 3s¹.” Its chemical symbol is Na. One unpaired electron can be found in the 3s orbital of the atom Na. Because of this, the three-electron-valence orbitals of Na are overlapping with this type of orbital, which has the same energy as that of molecular orbitals in the formation of molecules.

Atomic orbitals continue to combine in a similar manner throughout the process, resulting in the formation of a band. The “energy spread” of this band is determined by the energy difference that exists between the highest energy “antibonding orbital” and the strongest restrained “bonding orbital” in the band.

When the energy band gap between the conduction and valence bands is sufficiently large, the electrons are unable to make the transition from the valence band to the conduction band in a variety of circumstances. They are similar to these compounds in that they have significantly less or no conductivity. For example, in glass, when the energy band gap between the conduction and valence bands is small in size, a few electrons may be able to make the transition from the valence band to the conduction band, resulting in a small amount of conductivity being displayed. Semiconductors are a class of substances that fall into this category. For example Si, Ge (Silicon and Germanium respectively).

The Valence Band and Conduction Band Are The Two Bands That Make Up The Band Theory Of Metals  

It is also referred to as the band theory of solids or the zone theory of solids, depending on who you ask. It distinguishes between conductors, semiconductors, and insulators in a very clear and definite manner. Before you can comprehend the band theory, you must first become familiar with the following terms Those valence shell orbitals that have electrons in them are referred to as the Valence Band in this context. For example, the valence band of sodium is composed of three 3s¹ orbitals. Nitric acid has the electronic configuration of 1s², 2s², 2p⁶, 3s¹, and 3s². The conduction band is made up of electron orbitals that are either in the valence shell or in a higher unoccupied shell and are therefore unoccupied by electrons. As a result, the orbitals of the conduction band are completely devoid of matter. Again, let us consider the case of sodium, which has an empty orbital 3p after orbital 3s, resulting in the formation of a conduction band. In other words, we can say that the valence band is the highest energy band that has been completely filled. The conduction band is the name given to the next available band in the energy structure that is not filled with anything.

Conductors, Insulators, And Semiconductors The Theory Of Bands

Conductors  

There are no band gaps between the conduction and valence bands in a conductor. Conduction and valence bands in some metals partially overlap. The valence band and the conduction band are open to electron movement.

Only a portion of the conduction band has been occupied. This indicates that electrons have places to go. When electrons from the valence band move into the conduction band, they are free to roam about the device. Conduction is now possible.

Semiconductors  

The gap between the valence and conduction bands in a semiconductor is smaller. Electrons can be transferred from the valence band to the conduction band at normal temperature. It’s possible to conduct electricity in this way.

There are more electrons in the conduction band at higher temperatures, resulting in an increase in conductivity.

Insulators  

The valence band and conduction band are separated by a wide distance in an insulator.

When there aren’t any electrons moving up to the conduction band, the valence band is at capacity. This means that there’s no conduction band.

There are no electrons present in an insulator’s conduction band, and as a result, the material is unable to conduct.

From Orbitals to Bands  

Solids’ electrical and optical properties can be explained by the energy levels of atoms and molecules. Introduced are the terms Bravais lattice and Brillouin zone, and it is emphasised for covalent solids that the role of the chemical bond in the band structure (C, Si, Ge).

Conclusion  

Metals conduct electricity with the help of valence electrons, which are present in the metal. The atomic orbitals or electron cloud of metals have the same energy, which combines to form molecular orbitals whose energies are closer to one another, resulting in the formation of the ‘band’ of metals.There are no band gaps between the conduction and valence bands in a conductor. Conduction and valence bands in some metals partially overlap.