Lynn Sale, age 10, of Louisville, Kentucky, for her question:

What exactly is nitrogen?

We live in an invisible ocean of nitrogen, and furthermore we never get a good look at the nitrogen locked in the earth's rocks. There is also nitrogen in all plants and animals, though most of us would fail to recognize it. This strange, invisible chemical also helps to create many useful products. It may be in the form of a pain killing anesthetic or it may play a very different role in a house cleaning product. Nitrogen is in some of the farmer's best fertilizers, and it is a necessary ingredient in explosive mixtures such as dynamite.

A list of the earth's chemicals is very long and each one of them has a story of its own. The whole subject of chemistry seems like a very complex subject and very bewildering. But a beginner can get a good start by probing the secrets of just one chemical, and nitrogen is an excellent one to choose. The first mystery is that we never see nitrogen, even though it is one of our planet's most plentiful chemical elements.

There are reasons for its invisibility. At ordinary earth temperatures, nitrogen boils and its atoms separate and become gas. There are 12 ounces of nitrogen gas in every pound of air and tons of invisible nitrogen press down on every square mile of the earth's surface. Almost all the rest of the air is oxygen.   approximately one fourth. This presence of oxygen prevents nitrogen from burning so rapidly because the oxygen acts on the nitrogen to increase its boiling temperature.

All atoms, of course, have orbiting electrons. The nitrogen atom has two electrons in its inner shell and it needs five more to complete its second shell. In the air, it solves this problem by sharing as many as five electrons with another nitroger atom. The pair form a molecule, strongly tied together with electron bonds. For this reason, gaseous nitrogen is very unlikely to team up with other atoms and molecules. When it was first discovered in the 1700's, it was named azote, meaning lifeless, because it seemed to stay aloof from all the other busy chemical activities going on in the universe.

How wrong this idea was. We now know that the living cells of all plants and animals use nitrogen, and we also know how they get it. For instance, the energy of lightning makes the nitrogen in the air combine with atoms of oxygen. Together they form chemical compounds called nitrites that fall with the rain and sink into the soil. In the soil they are combined with sodium and other chemicals to form nitrates    and nitrates are soaked up as plant food. Animals get the nitrogen they need by eating plants, and so do we. When plants and animals decay, their complex nitrogen chemicals are changed by bacteria. Some of the nitrogen escapes back into the air but most of it is remodeled into useable plant food. This nitrogen cycle goes on behind the scenes. Also behind the scenes, nitrogen works with other chemicals to perform countless jobs in industry.

Nitrogen atoms also combine with hydrogen atoms to form ammonia, which is used to make tons of sulphuric acid used in industry. There are dozens of other useful compounds of nitrogen and various other chemicals. Some are used to make dyes,. some are rich plant fertilizers. A compound of nitrogen and boron is used to create a man made gem that rivals the diamond.