Metals, Conductors and semiconductors

We must have seen the wires and cables that are used in our home appliances.

The wire has a metal inside a PVC insulating covering.

Let us know why metal and insulated coverings are used in a wire.

The metal wire conducts an electric current while the insulator prevents electric shock.

Before we learn about conductors and insulators let’s begin with solids.

Solid is one of the states of matter in which the intermolecular space is very small.

Solids can be classified based on the following two properties: 1. Conductivity 2. Energy bandgap

Let us now learn about Conductivity

Conductivity is a measure of ease at which an electric charge or heat can pass through a material.

So, now we learn the Classifications based on conductivity.

On the basis of conductivity, solids fall into 3 categories. 1- Metals 2- Insulators 3- semiconductors.

Metals have very high conductivity i.e. in the range of to S/m

Insulators have very low conductivity i.e. in the range of to S/m

Semiconductors have a conductivity between those of metals and insulators, and it is in the range of to S/m

Let us now discuss Energy Band Gap

In solids, each electron has a unique position and surrounded by a different pattern of charges, therefore they will have different energy levels.

In solids, each electron has a These energy levels with continuous energy variation forms an energy band.

The energy band which includes energy levels of valence electrons is known as Valence Band and energy band above it is known as Conduction Band.

The gap between a conduction band and a valence band is called Energy Band Gap.

Now let’s see the classification based on the energy bandgap.

Solid can also be classified on the basis of the energy bandgap as metals, semiconductors, and insulators.

Metals:- In these solids, energy band gap is very low (Negligible).

Insulators:- In these solids, the energy band gap is very high (>3 eV).

Semiconductors:- In these solids, energy bandgap is in between those of metals and insulators (~1 eV).

Let’s have a look at some examples of metals, insulators, and semiconductors.

Examples of metals:- Iron, Silver, Gold, etc.

Examples of insulators:- Rubber, Glass, Plastic, Wood, etc.

Examples of Semiconductors are silicon, germanium etc and they have a wide application in electronic industries.


Solids can be divided into 3 categories based on their conductivity and energy bandgap.

They are, Metals Insulators Semiconductors.

The End