Billy Jefferson, ago 14, of Seattle, Wash., for the question:

What exactly is salt?

Salt is the name given to a whole list of chemicals. The salty sea contains magnesium chloride, magnesium sulphate, calcium sulphate and potassium sulphate   all of them chemical salts. Sodium chloride, however, accounts for more than three quarters of the salts in the sea  and this is what we normally call salt, meaning ordinary table salt.

All salts follow the same chemical patterns as table salt. They are formed in the same manner and they have certain chemical properties in common. Each is formed when an acid reacts with an alkali base. As a group, they have quite a high melting point. When melted, they are good conductors of electricity. Those that can be dissolved in water form a solution which is also a good conductor of electricity.

The term sodium chloride tells us that this salt is a compound of the elements sodium and chlorine. Its formation gives an excellent example of how elements combine to form compounds. Each molecule of salt is a unit of one atom of sodium and one atom of chlorine. Quantities of these salt molecules form a compound which is quite unlike its parent elements.

 Sodium is an alkali metal, silvery in color and so soft that it can be cut like butters  In nature, this element is never found in pure form. It is so active that it must be kept from both air and water and in the laboratory it is usually placed kerosene.

The element chlorine is a yellowish, suffocating gas, poisonous in large doses. Chemically it is known as a halogen, or salt former.

Atoms of sodium and chlorine combine to make salt because of their atomic structures. A normal atom has an equal number of protons and electrons. The electrons are the negatively charged particles which orbit the positive neutrons in the nucleus.

Electrons orbit the nucleus in shells„ Each shell has a quota of electrons   two fill the inner shell, eight the second. The third sell is complete with either sight or eighteen electrons.

The sodium atom has 11 electrons   two complete inside shells and one lone ranger electron in the third shell. The chlorine atom has 17 electrons   two complete inner shells and one short of a complete third shell. There is a place here for that lone ranger in the outer shell of the sodium atom. All we have to do is to expose the ;two elements to. each other.

We put a little wad of sodium into a jar of gaseous chlorine. Atoms of chlorine and sodium combine to make molecules of salt. The lone ranger in the sodium atom leaps into the outer ring of the chlorine atom  this unites the two moms in a molecules

The salt molecules thus formed tend to stick together end form crystals, Under a microscope, these crystals look like miniature ice cubes. Countless numbers of these crystals form a grain of salt. In this grain of salt, the number of molecules may be ten, followed by 24 zeros.