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why the conduction band & valence band are over laped each other for conductor?

why the conduction band & valence band are over laped each other for conductor?


2 Answers

879 Points
9 years ago

Dear student,

In an isolated atom the valence electrons can exist only in one of the allowed orbitals each of a sharply defined energy called energy levels. But when two atoms are brought nearer to each other, there are alterations in energy levels and they spread in the form of bands.
Energy bands are of following types

Valence band:

The energy band formed by a series of energy levels containing valence electrons is known as valence band. At 0 K, the electrons fills the energy levels in valence band starting from lowest one.

(i) This band is always filled by electrons.
(ii) This is the band of maximum energy.
(iii) Electrons are not capable of gaining energy from external electric field.
(iv) No flow of current due to such electrons.
(v) The highest energy level which can be occupied by an electron in valence band at 0 K is called Fermi level.

Conduction band:

The higher energy level band is called the conduction band.

(i) It is also called empty band of minimum energy.
(ii) This band is partially filled by the electrons.
(iii) In this band the electrons can gain energy from external electric field.
(iv) The electrons in the conduction band are called the free electrons. They are able to move anywhere within the volume of the solid.
(v) Current flows due to such electrons.

Godfrey Classic Prince
633 Points
9 years ago

Dear Sudip Mistry,

The Conduction Band & Valence Band are overlapped in case of a conductor because the electrons in the Valence band can easily move into the conduction band & vice versa and thus conduct electricity which is the characteristic property of the conductors !!

In case of Semi-Conductors the Valence Band & Conduction band are seperted by a small gap & so only a few elctrons can jump across the gap into the Conduction band (or) vice versa & thus conduct electricity partially !!


In case of Insulators(Non-Condutors) the Valence Band & Conduction Band are seperated by a large gap & so it is impossible for the electrons to cross this gap & move to the Conduction Band (or) vice versa thus conducting electricity .Thus it does not conduct electricity !


Hope you understood now ..

All the Best & Good Luck !!

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