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Chemistry > The Solid State > Electrical Properties of Solids
The Solid State

Electrical Properties of Solids

We are aware of the physical properties of solids. Like the fact that they have a definite shape and volume. But the electrical properties of solids vary largely based on their composition and chemical structure. They are divided into three groups – conductors, semiconductors, and insulators. Let us study these further.

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Electrical Properties of Solids

Now the electrical property of a substance is a reference to its conductivity. Electric Conductivity of a substance is defined as its ability to transmit heat energy or electric energy (and in some cases also sound energy). So a good conductor of electricity is easily able to transmit the energy without boiling or melting or changing its composition in any way.

Solids have varying degrees of conductivity i.e. all solids do not have uniform electrical properties. Actually, solids can be divided into three broad categories based on their electrical conductivity. These three groups are as follows,

Conductors

Broadly speaking, conductors are solids that have good electrical conductivity. They allow heat energy and electric currents to transmit through them with ease and speed. Conductors allow this transfer of energy to happen via free flow of electrons from atom to atom. They have the ability to carry this energy throughout themselves even when the current is only applied to one part of their body.

All metals are known to be the best conductors. Their conductivity depends on the number of valence electrons of their atoms. These electrons are not closely bound together and can move freely. Metals have such electrons in their atoms, and so they conduct heat and electricity so well. Metals allow the electric field to transmit through them in conductivities order of 106 – 108 ohm-1.

Insulators

Semiconductors and Insulation

Stark opposite to conductors, insulators are materials that absolutely do not conduct any electric energy or currents. They do not let any (or very little) electric charge flow through them. They have a significant band gap which prevents the flow of electricity. Some examples are glass, wood, plastics, rubber etc.

Since insulators are very bad conductors they have another use. We use them to insulate conductors and semiconductors. For example, you must have seen copper wires with a covering of plastic or some form of polymers. They protect the wires and cables without allowing the electric current to go through them. This is insulation of the wire.

Semiconductors

Semiconductors are the go-between conductors and insulators. These are solids that have the ability to conduct electricity through them but only under certain conditions. There are two such conditions that affect the ability of semiconductors to conduct energy, heat, and impurities.

  • Intrinsic Semiconductor: These are pure materials with no impurities added, so they are known as undoped semiconductors. Here we apply thermal energy to the material and create vacancies in the valence bands. This allows the energy to pass through. And yet these are not very good conductors and find very limited applications
  • Extrinsic Semiconductors: These are doped semiconductors. We add certain impurities to increase the conductivity of the materials. There are two types of extrinsic semiconductor, namely n-type and p-type. Examples are when we boost the conductivity of silicon and germanium by this method.

One reason why semiconductors are an important material is that we have control over their conductivity. This is why they find many applications, especially in electronics.

Solved Question for You

Q: Conductivity of semiconductor increases with increase in temperature. True or False?

Ans; The given statement is True.

  • Intrinsic semiconductor; conductivity goes up or resistivity goes down with temperature goes up.
  • Heavily doped conductivity turns up again or resistivity goes down with temperature goes up.
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