1. Composition of Matter

All activity in any type of electrical circuit depends on the behavior of tiny electrical charges called electrons. To understand the behavior of electrons, we must investigate the composition of matter. The electron is one of the basic electrical components of all matter.


All matter, regardless of its state (solids, liquids, and gases), is made up of tiny particles known as atoms. Atoms combine in small groups of two or more to form molecules; however, when atoms are divided, smaller particles are created. These particles have positive or negative electrical charges.

There are just over 100 different basic materials in the universe, and millions of different compounds can be formed from them. These basic materials are called elements. Iron, copper, aluminum, oxygen, hydrogen, and mercury are examples of elements. The basic particles that make up all the elements, and thus the entire universe, are called protons, electrons, and neutrons. A proton is the basic particle having a single positive charge; therefore, a group of protons produces a positive electrical charge. An electron is the basic particle having a single negative charge; therefore, a group of electrons produces a negative electrical charge. A neutron is the basic particle having no charge; therefore, a group of neutrons would have no charge.

The construction of atoms of the various elements can be examined starting with the simplest of all—hydrogen. The atom of hydrogen consists of one proton, around which one electron circles (Figure 6-1).

Figure 6-1 — Hydrogen atom.

There is an attraction between the two particles because negative and positive electrical charges always attract each other. Opposing the attraction between the two particles, and thus preventing the electron from moving into the proton, is the centrifugal force on the electron caused by its circular path around the proton. This same sort of balance is produced if a ball tied to string is whirled in a circle in the air. The centrifugal force exerted tries to move the ball out of its circular path but is balanced by the string (the attractive force). If the string should break, the centrifugal force would cause the ball to fly away.

Actually, this is what happens at times with atoms. The attractive force between the electron and proton sometimes is not great enough to hold the electron in its circular path and the electron breaks away.

In an atom, unlike electrical charges attract and like electrical charges repel each other. Electrons repel electrons and protons repel protons, except when neutrons are present. Though neutrons have no electrical charge, they do have the ability to cancel out the repelling forces between protons in an atomic nucleus and thus hold the nucleus together.

Composition of Electricity

When there are more than two electrons in an atom, they move about the nucleus in different orbits which are referred to as shells (Figure 6-2). The innermost shells of the atom contain electrons that are not easily freed and are referred to as bound electrons. The outermost shell contains what is referred to as free electrons. These free electrons differ from bound electrons in that they can be moved readily from their orbit.

Figure 6-2 — Composition of an atom.

If a point that has an excess of electrons (negative) is connected to a point that has a shortage of electrons (positive), a flow of electrons (electrical current) will flow through the connector (conductor) until an equal amount of electrical charge exists between the two points.

Electron Theory of Electricity

A charge of electricity is formed when numerous electrons break free of their atoms and gather in one area. When the electrons begin to move in one direction (as along a wire, for example), the effect is a flow of electricity or an electric current. Actually, electric generators and batteries could be called electron pumps, because they remove electrons from one part of an electric circuit and concentrate them in another part of the circuit. For example, a generator takes electrons away from the positive terminal and concentrates them at the negative terminal. Because the electrons repel each other (like electrical charges repel), the electrons push out through the circuit and flow to the positive terminal (unlike electrical charges attract). Thus we can see that an electric current is actually a flow of electrons from a negative terminal to a positive terminal.

Test your Knowledge

1. All matter is made up of tiny particles known by what term?

A. Protons
B. Electrons
C. Neutrons
D. Atoms