Classification Of Solid And Energy Band.

This post is further extension of previous posts,” Understand The Atomic Structure..." and "Different Types of Energy Band..."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 behavior 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 behavior 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 acquire 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 behave 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 have negative temperature co-efficient of resistance.

Refer all three posts for complete information on atomic structure.

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Different Types of Energy Band In An Atom Of Solid.

This post is further extension of previous post” Understand The Atomic Structure..."Here you will find the information about energy band of an atom.

In case of single isolated atom, the electrons any orbit posses definite energy. However, an atom in a solid is greatly influenced by the closely packed Neighboring atoms, that’s why the electron in any orbit of such an atom can have arranged of energies rather than the single energy. So, the range of energies Is known as "Energy Band”. In other word we may say that,” The range of energies possessed by an electron in a solid is known as energy band".

When the atom in a solid, the electron in any orbit can have a range of energies. For instance, electron in the first orbit has slightly different energies Because no two electrons in this orbit see exactly the same charge environment. Since, there are millions of first orbit electrons, the slightly different energy Level forms a band, called first energy band. Similarly, second orbit electrons form second energy band and so on. Below are the important energy bands in Solid.

01) Valence Band: -
The range of energies (Band) possessed by the valence electrons is known as valence band. The electron in the out most orbit of an atom is known as
Valence electrons. In a normal atom, valence band has the electrons of highest energy. This band may be completely or partially filled. For example, in case of Inert gases, the valence band is full where as for other materials, it is only partially filled and accommodate more electrons.

02) Conduction Band: -
In certain materials, the valence electrons are loosely attached to the nucleus. Even at room temperature, some of the valence electrons may be detached to Become free electrons and which are responsible for conduction of current in a conductor. Because of this, these free electrons are called as conduction Electrons. The range of energies (Band) possessed by conduction band electrons is known as conduction band. All electrons in conduction band are free Electrons. If a substance has empty conduction band, it means current conduction is not possible in that substance. For example, Insulators.

03) Forbidden Energy Gap: -
The separation between conduction band and valence band on energy level diagram is known as forbidden energy gap as there is no allowed energy state In this region. The greater the energy gap, more tightly the valence electrons are bound to the nucleus. We can push an electron from valence band to Conduction band by supplying the extra energy equal to the forbidden energy gap.

I hope, this information will help you in electronics field. Classification of solid and energy band will be cover in next post.

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