Classification of Solids Based on Energy Bands

Conductors are materials that allow the flow of electric charge, also known as electric current. The most common conductors are made of metal. Such materials allow current to flow due to the presence of free electrons or ions that begin to move when voltage is applied. The electrical resistance of the conductor is comparatively low and increases as the temperature rises.

Semiconductors are materials that conduct electricity between conductors and insulators. You can block or allow the flow of electricity to gain complete control over the flow of electricity. They are mainly modified by adding impurities, which is called doping. This changes characteristics such as unidirectional current flow, amplification, and energy transformation. Electrical conduction in a semiconductor is based on the movement of electrons and positions (holes).

Insulators are materials that have very high electrical resistance and do not carry current. Since the insulator has no free electrons, it does not conduct electricity. Therefore, they help protect against impact.

Band theory 

The most popular explanation for discrepancies in conduction is band theory. The ‘band’ of a material is used for explaining a variation in its physical properties of conduction.

Within the limits of energy, electrons orbit the positive nucleus of a single atom. Energy levels in many atoms reorganise into two bands, the valence band and the conductive band. The lower level of electrons is in the valence band, and the higher level of electrons is in the conduction band.

There is an energy gap between the bands where electrons cannot exist. Electrons move when conduction occurs, and for this to happen, there must be spaces in the energy bands for the electrons to move into.

Classification of solids based on energy bands 

1. Conductors 

Definition

Conductors are materials that allow current to flow easily.

When conductors and semiconductors are compared, conductors enable better current flow, and are said to be good electrical conductors.

Categories of conductors 

1. Metals

Most conductive materials used in practical applications are metals. For example, the wiring used in a house probably employs copper wire or its alloy as a conductive material. The electric plug contains metal, and the internal mechanism of the electric iron also uses metal as a conductive material. This is because metals have many free electrons and promote mobility. A few of the best metal conductors are silver (Ag), copper (Cu), and gold (Au). 

1. Nonmetals

 Some nonmetals are very good conductors of electrical energy. For example, carbon in the form of graphite is a very good conductor. Looking at the structure of graphite, only three of the four carbon atoms are used for bonding. This releases the electrons and binds them together. Most nonmetals are poor conductors of electricity.

1. Ionic conductors

Conductors in a solution form are known as ionic conductors. For example, saltwater is an ionic solution and is an excellent electrical conductor.

2. Semiconductors

Definition

Semiconductors are materials that exhibit conductivity between conductors or metals and non-conductors or insulators. Semiconductors are mixtures such as gallium arsenide or pure components such as germanium and silicon.

Categories of semiconductors 

1. Intrinsic semiconductors: Intrinsic semiconductor materials are chemically very purely made. They consist of only one element type. When the temperature rises due to collision, some electrons move freely in the lattice without being bound and do not exist in their original positions (holes). These free electrons and holes contribute to the conduction of electricity in the semiconductor. The number of negative and positive charge carriers is the same.
2. Extrinsic semiconductors: The conductivity of semiconductors can be significantly improved by introducing a small number of suitable surrogate atoms called impurities. The process of adding foreign atoms to a pure semiconductor is called doping. 

3. Insulators 

Definition

Electrical insulators are different from conductors. Conductors are materials that propagate the ease of current flowing through them. They allow charges to flow easily. Insulators, on the other hand, are materials that do not allow electric charges to flow freely.

Application 

Insulators are primarily used when it is necessary to prevent the flow of charge. These materials act as effective insulators because they do not have the moving charge required to propagate the current. Electrical insulators are mainly used as parts of electrical equipment.

Conclusion 

While the classification of solids is done based on band energy into conductors, semiconductors, and insulators, they all have their respective applications in different fields. Examples of conductors are gold, silver, aluminium, and copper; semiconductors are gallium arsenide, germanium, and silicon; and insulators include rubber, plastic, wax, and wood.