Molecules are made up of smaller particles called ATOMS. An atom is the smallest particle of an element that retains the characteristics of that element. The atom of one element, however, differs from the atoms of all other elements, Since over 100 elements are known, there must be over 100 different atoms, or a different atom for each element. Just as thousands of words are made by a combination of the proper letters of the alphabet, so thousands of different materials are made by the chemical combination of the proper atoms. Any particle that is a chemical combination of two or more atoms is called a molecule. The oxygen molecule has two atoms of oxygen, and the hydrogen molecule has two molecules of hydrogen. Sugar, on the other hand, is a compound composed of atoms of carbon, hydrogen, and oxygen. These atoms are combined into sugar molecules. Since the sugar molecules can be broken down by chemical means into smaller and simpler units, we cannot have sugar atoms.

In Figure 2-1 you will see that the atoms of each element are made up of electrons, protons, and, in most cases, neutrons, which are collectively called subatomic particles. Furthermore, the electrons, protons, and neutrons of one element are identical to those of any other element. The reason there are different elements is that the number and arrangement of electrons and protons within the atom are different for the different elements.

The electron is considered to be a small negative charge of electricity. The proton has a positive charge of electricity equal and opposite to the charge of the electron. Scientists have measured the mass and size of the electron and proton. They know how much charge each has. The electron and proton each have the same quantity of charge, although the mass of the proton is about 1837 times that of the electron. In some atoms, a neutral particle exists called a neutron. The neutron is a mass about equal to that of a proton, but it has no electrical charge. According to a popular theory, the electrons, protons, and neutrons of the atoms are thought to be arranged in a manner similar to a miniature solar system. The protons and neutrons form a heavy nucleus with a positive charge, around which the very light electrons revolve.

Figure 2-1.-Structure of simple atoms.

Figure 2-1 shows one hydrogen and one helium atom. Each has a relatively simple structure. The hydrogen atom has only one proton in the nucleus with one electron rotating about it. The helium atom is a little more complex. It has a nucleus made up of two protons and two neutrons, with two electrons rotating about the nucleus. Elements are classified numerically according to the complexity of their atoms. The atomic number of an atom is determined by the number of protons in its nucleus.

In a neutral state, an atom contains an equal number of protons and electrons. Therefore, an atom of hydrogen, which contains one proton and one electron, has an atomic number of 1; and helium, with two protons and two electrons, has an atomic number of 2. The complexity of atomic structure increases with the number of protons and electrons.

MAGNETISM

To understand properly the principles of how electrical equipment produces work, you must understand magnetism, the effects of magnetism on electrical equipment, and the relationship of the different properties of electricity. Magnetism and electricity are so closely related that the study of either subject would be incomplete without at least a basic knowledge of the other.

Much of today's electrical and electronic equipment could not function without magnetism. Computers, tape recorders, and video reproduction equipment use magnetic tape. High fidelity speakers use magnets to convert amplifier outputs into audible sound. Electric motors use magnets to convert mechanical motion into electrical energy. Magnetism is generally defined as that property of a material that enables it to attract pieces of iron. Material with this property is known as MAGNETIC. The word magnetic originated from the ancient Greeks, who found stones possessing this characteristic. Materials that are attracted by a magnet, such as iron, steel, nickel, and cobalt, have the ability to become magnetized. Thus they are magnetic materials. Materials, such as paper, wood, glass, or tin, which are not attracted by magnets, are considered nonmagnetic. Nonmagnetic materials

Figure 2-2.-The effect of current.

are not able to become magnetized. You will find additional information on the basic principles of magnetism in the Navy Electricity and Electronics Training Series (NEETS), module 1, NAVEDTRA 172-01-00-88, chapter 1.