Class 12 > Unit # 21:Physics of Solids > Energy Bands in Conductors, Insulators and Semi conductors

Classification of Conductors, Insulators, and Semiconductors Using Energy Bands in Solids

Energy Bands in Solids: When isolated atoms come together to form a solid, interactions between neighboring atoms cause the electron energy levels to split and overlap, creating continuous energy bands. There are three types of bands:

1. Valence Band: The valence band is the range of energy levels occupied by electrons that are bound to atoms and participate in chemical bonding. It is the highest energy band that contains electrons under normal conditions.

2. Forbidden Band (Energy Gap): The forbidden band, or energy gap, is the range of energy levels between the valence band and the conduction band where no electron states exist. This gap influences the material's electrical properties; a larger gap typically means the material is less conductive.

3. Conduction Band: The conduction band is the range of energy levels where electrons are free to move throughout the material, allowing electrical conduction. Electrons in the conduction band are not bound to any particular atom and can carry electric current through the solid.

Detailed Video Lecture

Depending on their electrical conductivity and energy band structures, solids are classified into three main categories: Conductors, Semiconductors, and Insulators.

(Ensure your diagram clearly illustrates the Valence Band, Forbidden Gap, and Conduction Band for Conductors, Insulators, and Semiconductors)

1. Conductors: There is no gap (or an overlap) between the conduction band and the valence band. Thus, electrons can easily flow from the valence band to the conduction band under the influence of an electric field, making them good conductors of electricity.

2. Insulators: These materials do not conduct electricity under normal conditions. The band gap between the valence band and conduction band is very large. Even if a large amount of energy is provided to these solids, they do not conduct electricity (e.g., wood, plastics, etc.).

3. Semiconductors: The gap between the conduction band and the valence band is very small; therefore, whenever sufficient energy is provided to the electrons in a semiconductor, electrons jump from the valence band to the conduction band. The conductivity of semiconductors increases with an increase in temperature.