David Mannering, Age 12, Of Smith Center, Kan., for his question:

What is neon?

The razzle dazzle lights in the downtown shopping district are called neon signs  though not all of them are made from pure neon gas. Only the brilliant red signs are made from tubes filled with pure neon. Some have neon mixed with other gases. The recipe for those vivid blue lights, for example, has a little mercury added to the neon.

The word neon means new, though there have been traces of neon gas in the earth's atmosphere since time began. Chemists discovered the nitrogen and oxygen that make up 99% of the air long ago. They also learned that most of the remaining 1% is carbon dioxide. The group of rare gases that makes up the final trace of the atmosphere was not discovered until the turn of the century  and one of them was named neon, the new one.

These trace gases are inert, which means they do not combine readily with other elements to form compounds. This makes them hard to identify and explains why the chemists took so long to find them. But when heated and viewed through the spectrograph, each of the rare gases reveals its own particular color. Their names are argon, meaning the lazy one; krypton, the hidden one; xenon, the stranger, and, of course, neon, the new one.

Recently, science has found that the inert rare gases are not so inert as we thought. Xenon and radon will combine with each other when heated to a mere 300 centigrade degrees. The compound of crystals has been named xenontrafluoride, it may be that other rare gases will also form compounds under the right conditions.

There is a reason why the inert gases are reluctant to team up with atoms of other elments. A busy atom, such as oxygen, is always trying to borrow or share electrons. The electrons of an atom are arranged in orderly she1ls. The inner shell is comp1ete with two electrons; the second and third shells are complete with eight electrons apiece. The busy atoms, such as oxygen, have incomplete electron shells.  In seeking to fill they share electrons with other atoms, and in so doing they form molecules of compounds.

Each of the inert gases has all its shells of electrons complete. It does not need to borrow or share extra electrons with atoms of other elements. Neon has two electron shells. Its inner shell is complete with two, and its second shell is complete with eight electrons. Its 10 electrons means that it has 10 protons in its nucleus and its atomic number is 10.

Neon is expensive to extract from the air, but a small amount of it is enough to light a eat many vivid neon signs. Ordinary air is extracted from the glass tube and rep1aced with neon. An electrode is sealed in each end of the tube, and the electric current jumps from one electrode to the other. This agitates the atoms of neon gas and causes them to glow with a red light vivid enough to be seen at high noon or even through a fog.