Anthony Trapane, age 12, of Gary, Ind., for his question:

What are atomic numbers?

Everything in the world is made from tiny atoms. So also are our sister planets, the sun, the moon and all the stars. The number of atoms is beyond imagination. But the number of different atoms is quite small. In our world of nature, there are only 92 different atoms. A few more have been found by the scientists and maybe others exist in the seething stare. In quantity, atoms of one kind form an element. The element gold is made only from atoms of gold. Oxygen is an element and carbon is an element ‑ and every element is labeled with its own atomic number.

The atomic number of, say, the element gold is built right into every ;tom of gold. Every atom is made from still smaller atomic particles. Every atom contains one or more proton particles. Every atom of gold contains 79 protons, every atom of oxygen contains eight protons. This is where an element gets its atomic number. The atomic number of gold is 79, the atomic number of oxygen is 8. Every atom of carbon in the universe contains six protons, which is why the atomic number of carbon is 6.

The atomic numbers so far discovered run in a neat row all the way from 1 to 102. If you give an atomic number to a scientist, he can tell you a great deal about the element and its atoms. Light elements with small atoms have the low atomic numbers. Heavy elements with large atoms have the large atomic numbers. The atomic number also can tell the expert how the element behaves with other elements. He can tell all this and maybe more, because the number of protons is just about the most vital piece of information you can have about any atom.

The basic structure of any atom is a central nucleus surrounded by orbiting electrons. The electrons have particles charger with negative electricity. The protons, charged with positive electricity, are locked in the nucleus of the atom. The total atom is electrically neutral, for the positive and negative charges are evenly balanced. In other words, the number of protons equals the number of electrons and the atomic number tells us both.

The smallest atom is hydrogen, atomic number 1. One electron orbits ­the one proton in its nucleus. Helium, atomic number 2, has two protons and two electrons. It has a positive charge equal to that of two hydrogen atoms. The element lithium, atomic number 3, has three protons. One by one the atomic numbers get bigger. And so do the atoms The biggest atom in nature is uranium, with the atomic number 92. The largest atom discovered in the laboratory has atomic number 102. The big atoms tend to be unstable; They are the radioactive ones, in the process of breaking apart into smaller atoms,