Engineering materials can be divided into three groups, according to their electrical conductivity. The first group is the group of conductors which are materials that let electrical current flow through them. Most of the conductors are metals, because of the metallic bond that is formed between their atoms, resulting in the existence of many free electrons. This is why they are used in making cables. The second group are the insulators, materials that let very little or no electrical current flow through them. This happens because their atoms are connected to each other via a covalent or an ionic bond and there are no free electrons, making the movement of charges much more difficult, due to their large mass. These materials are often used in wrapping the cables for safety reasons. Finally, the third group are the semiconductors which have variable conductivity, depending on the conditions. Their conductivity increases with increasing temperature and that property has made them very popular. Semiconductors are the reason why we have all electronic devices today and are used heavily in making them. All engineering materials are very useful in electrical and electronic applications,each one in its own way.
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