[Chemistry Class Notes] on Electrical Properties of Solids Pdf for Exam

One of the four essential states of matter is solid (the others being liquid, gas and plasma). In a solid, the molecules are packed tightly together and have the least amount of kinetic energy. Structural stability and resistance to a force applied to the surface characterise a solid. A solid material, unlike a liquid, does not flow to take on the form of its container, nor does it expand like a gas to fill the entire volume available.

There are physical as well as electrical properties of matter. Likewise, solids have definite shape and volume. However, depending on their composition and chemical structure, the electrical properties of solids differ to a large degree. Conductors, semiconductors and insulators are classified into three categories.

Electrical Properties of Solids 

Conductivity is referred to as the electrical property of a material. A substance’s electrical conductivity is characterised as its capacity to transmit heat energy or electrical energy (and in some cases also sound energy). Thus a good electricity conductor can easily transmit energy without boiling, melting or altering its composition in some way.

Solids have different degrees of conductivity, which means that all solids do not have uniform electrical properties. Currently, based on their electrical conductivity, solids can be classified into three different categories. The following are these three categories:

Conductors

Conductors are solids that have strong electrical conductivity. They allow heat energy and electric currents to transmit with ease and speed through them. Conductors allow this energy transfer to take place through free electron flow from atom to atom. When the current is just applied to one part of their body, they have the power to bring this energy all over themselves.

The strongest conductors are understood to be all metals. Their conductivity is dependent on their atoms’ number of valence electrons. Such electrons are not tightly bound together and are free to pass. Metals have electrons like this in their atoms, which is why they conduct heat and electricity so well. Metals allow the electric field to transmit in conductivity ranges from 106-108 ohm-1 through them.

Insulators

Unlike conductors, insulators are materials that do not conduct any electrical energy or currents at all. They do not allow any electric charge (or very little) to pass through them. They have a considerable bandgap that prevents electricity from flowing. Glass, wood, plastic, rubber, etc. are some examples.

Since insulators are very weak conductors, there is another use for them. In order to insulate conductors and semiconductors, we use them. You would have seen copper wires, for instance, covered with plastic or some sort of polymer. Without allowing the electric current to go through them, they secure the wires and cables. This is wire insulation.

Semiconductor

The one between conductors and insulators are semiconductors. These are solids that have the ability, but only under certain conditions, to conduct electricity through them. The ability of semiconductors to conduct energy, heat and impurities is impaired by two such conditions.

Intrinsic Semiconductor: These are pure materials, so they are classified as undoped semiconductors with no impurities added. We add thermal energy to the material here and create vacancies in the bands of valence. This makes it possible for the energy to move through. Yet, these conductors are not very strong and have very few applications Extrinsic Semiconductors: These are semiconductors with doping. To boost the conductivity of the products, we add some impurities. There are two kinds of extrinsic semiconductors: n-type and p-type, respectively. Examples are that through this technique, we increase the conductivity of silicon and germanium.

Semiconductors are the most important material due to its property that one can control the conductivity of semiconductors. Due to this reason, semiconductors are mostly found in electronics applications.

Thermal conductivity is nearly related to the electrical conductivity of a substance. We know that metals are good electrical conductors. For a solid to conduct heat, one molecule or atom movement needs to be easily transferred to its neighbour. This type of transfer is relatively easy because of the non-directional nature of the metallic bond, so metals conduct heat well. In a solid network, on the other hand, where the bonds are stiffer and the angles between the atoms are strictly defined, it is more difficult to transfer them. These solids are expected to have low heat conductivity and are known as heat insulators.