Michael Stones, Age 13, Of Salt Lake City, Utah, for his question:

What is an atomic number?

An atom is the smallest particle of an element. The nature of each atom depends upon the number of proton particles in its nucleus. This information is given to us in the atomic number. Hydrogen, the smallest atom., has the atomic number 1. The atomic number for gold is 79, and any atom that has 79 protons is an atom of gold.

We know of more than 100 different atoms, and we know a great deal about one of them. A wealth of this information is crowded into a chart which can be printed on a page of a book. This chart is the periodic table of elements. It shows all the known elements in lines running across and columns running down.

Each element is allotted its own square on the chart, and the basic information about its stoats is telescoped into a few letters or figures. The element is identified by its chemical symbol, which is one or two letters. The symbol for oxygen is 0; the symbol for osmium, which starts with the same letter, is Os. Cu is the symbol for cuprum, the latin name for copper.

There are two figures in a slot with each element. One is the mass number, which is the atomic weight. The atomic weight for helium is 1.0080; the atomic weight for carbon is 12.011. Oxygen is atomic weight 16, and gold is 197. Most, but not all, of the atomic weights are not whole numbers. The atomic number is always a whole number.

This is because the atomic number deals with whole particles. The atom, of course, is made from a wide assortment of different particles. The three main atomic particles are protons, neutrons and electrons. The protons and neutrons are locked in the nucleus of the atom, and the electrons swarm around the nucleus. The protons are electrically neutral, and. The number of these particles may vary without changing the atom.

The number of protons is constant in each element. On the periodic table, you see that they go all the way from one to more than 100. A proton is a unit of positive electricity, and an electron is an equal. Unit of negative electricity  and a normal atom has an equal number of protons and electrons. The atomic number of an element te11s how many protons are present in the nucleus, and when we know this, we also know the number of electrons in a normal atom of the element.

An atom, say., of gold, can lose or gain, swap or share a few electrons. But, so long as it has 79 protons, it is still an atom of gold. If it loses a proton, it becomes platinum  which has atomic number 78. If it gains a proton, it becomes mercury  which has atomic number 80.