All elements of which matter is made may be placed into one of three categories: CONDUCTORS, SEMI-CONDUCTORS, and INSULATORS, depending on their ability to transfer an electric current.
CONDUCTORS are elements which transfer electricity very readily, INSULATORS have an extremely high resistance to the flow of electricity.
All matter between these two extremes may be called SEMI-CONDUCTORS.
The electron theory states that all matter is composed of atoms and the atoms are composed of smaller particles called protons, electrons, and neutrons. The electrons orbit the nucleus which contains the protons and neutrons. It is the valence electrons that we are most concerned with in electricity. These are the electrons which are easiest to break loose from their parent atom. Normally, wires or runs have three or less valence electrons; insulators have five or more valence electrons; and semi-conductors usually have four valence electrons.
The electrical connectivity of matter is dependent upon the atomic structure of the material from which the wire or run is made. In any solid material, such as copper, the atoms which make up the molecular structure are bound firmly together. At room temperature, copper will contain a considerable amount of heat energy. Since heat energy is one method of removing electrons from their orbits, copper will contain many free electrons that can move from atom to atom. When not under the influence of an external force, these electrons move in a haphazard manner within the run. This movement is equalin all directions so that electrons are not lost or gained by any part of the run. When controlled by an external force, the electrons move generally in the same direction. The effect of this movement is felt almost instantly from one end of the wire or run to the other. This electron movement is called anELECTRIC CURRENT.
Some metals are better conductors of electricity than others. Silver, copper, gold, and aluminum are materials with many free electrons and make good conductors. Silver is the best conductor, followed by copper, gold, and aluminum. Copper is used more often than silver because of cost. Aluminum is usedwhere weight is a major consideration, such as in high-tension power lines, with long spans between supports. Gold is used where oxidation or corrosion is a consideration and a good conductivity is required. The ability of a conductor to handle current also depends upon its physical dimensions.
These electrical movers are usually found in the form of wire, but may be in the form of bars, tubes, or sheets. Non-conductors have few free electrons. These materials are called INSULATORS. Some examples of these materials are rubber, plastic, enamel, glass, dry wood, and mica.
Just as there is no perfect electrical mover, neither is there a perfect insulator.
materials are neither good movers nor good insulators, since their
electrical characteristics fall between those of movers and insulators.
These in-between materials are classified as SEMI-CONDUCTORS. Germanium
and silicon are two common types used in solid-state devices.