Classification Of Solid And Energy Band.

This post is further extension of previous posts,"Understand The Atomic Structure Through Bhor's Atomic Model."and "Different Types of Energy Band In An Atom Of Solid. ".

This post along with previous two posts will complete the information of "Atomic Structure."

We know that some solids are good conductors of electricity while others are insulators.There is also an intermediate class of semiconductors.The difference in the behaviour as regards their electric conductivity can be explained in terms of energy bands.The electrons in the lower energy band are lightly bound to the nucleus and play no part in conduction process.However,the valence and conduction bands are particularly important in ascertaining the electrical behaviour of various solids.

Solids are classified as below,

01)Insulators:-
Insulators are those substances which do not allow the passage of electric current through them.For example,wood,rubber,glass etc.In this,valence band is full but conduction band is empty.The energy gap between valence and conduction band is very large.that is why,a very high electric field is required to push the valence electrons to the conduction band.For this reason,the electric conductivity of such materials is nil under ordinary conditions.

At room temperature,the valence electrons of the insulators do not have enough energy to cross over to conduction band.Some of the valence electrons may acquired enough energy to cross over to the conduction band,if the temperature is raised sufficiently.Hence,the resistance of an insulator is decrease with increase in temperature.

02)Conductors:-
Conductors are those substances which easily allow the passage of electric current through them.For example,copper,aluminium.There are large number of free electrons are available in a conductor.In conductors,the valence and conduction band,overlap each other.Due to this overlapping,a slight potential difference across a conductor causes the free electrons to constitute electric current.

03)Semiconductors:-
Semiconductors are those substances whose electric conductivity lies between conductors and insulators.In this,the valence band is almost filled and conduction band is empty.The energy gap between valence and conduction band is very small.Therefore,comparatively smaller electric field is required to push the electrons from valence band to conduction band.

At low temperature,the valence band is completely full and conduction band is completely empty.Because of this,semiconductors behaves as an insulator at low temperature.As the temperature increases,more valence electrons cross over to the conduction band and the conductivity increases.It means,semiconductors has negative temperature co-efficient of resistance.

Refer all three posts for complete information on atomic structure.

You may also interested in following..........
Understand The Atomic Structure Through Bhor's Atomic Model.
Different Types of Energy Band In An Atom Of Solid.
What are the different types of materials used for Semiconductors.