Question

Explain the classification of conductors, insulators, and semiconductors on the basis of energy bands.

Hint:

The electrical conductivity of materials is determined by the size of the energy gap between their conduction band and valence band.

Answer 1

Step 1: Conductors.
In conductors, the conduction band and valence band overlap or are very close. Electrons in the valence band can easily move to the conduction band when a small electric field is applied, allowing current to flow. Hence, conductors have free electrons and exhibit high electrical conductivity. Materials like copper, aluminum, and silver are examples of conductors.
Step 2: Insulators.
In insulators, the conduction band and valence band are separated by a large energy gap. This large gap makes it extremely difficult for electrons to move from the valence band to the conduction band. As a result, insulators have very low electrical conductivity. Materials like rubber, wood, and glass are examples of insulators.
Step 3: Semiconductors.
Semiconductors have a small energy gap between the conduction band and the valence band. At absolute zero temperature, they behave like insulators, but at higher temperatures, some electrons gain enough energy to jump into the conduction band. This allows semiconductors to conduct electricity, but not as well as conductors. Materials like silicon and germanium are examples of semiconductors.
Step 4: Conclusion.
The classification of materials into conductors, insulators, and semiconductors depends on the energy gap between the conduction band and the valence band.