Sherry Hays, age 13, of Oalcridgey Ore,, for her question:

This is the Atomic Age, the period of history in which mankind probed the secrets of the tiny atom, unleashed its energy and learned to tame this atomic energy to do useful work, Since we live in this staggering age, it is natural to wonder about the nature of the tiny atom and, perhaps, how it was discovered  The story begins some 2,500 years ago when the Greek philosopher‑scientists were wondering about the nature of matter ‑ why objects change and decay, break apart and form new objects,

These thinkers could not use electricity and had none of our modern equipment with which to solve their problems  They observed and noted what they saw and reached their conclusions by using their logic, their mathematics and their common sense  In 460 B  C Democritus of Greece reported that all matter must be made of tiny particles which could not be divided into smaller particles  We call these particles atoms, from Greek words meaning uncut or indivisible 

For more than 2,000 years, very little was added to the atomic theory of Democritus  An atom was known to be too small to be seen, but scientists began to suspect that there were only a few different atoms  Then, in 1802, John Dalton showed that two or more types of atoms combine to make something quite different, Table salt, as we know, is a compound of sodium and chlorine atoms, A few basin atoms can form countless different compounds  Compounds can also break apart into separate atoms  The old theory that objects change because they are made of atoms was now partly explained,

Science then learned that the atom was electrical in nature, Radio  activity showed that atoms themselves break apart, The atom then must be made of small, pro7uably electrical, particles 

With this informations the structure of the atom was soon salved: More than 100 different atoms have note been identified, sorted and arranged in a wonderful Periodic Table 

The heart of an atom is its central nucleus charged with positive electricity  It is a wad of protons, each adding a single charge of positive electricity, and neutrons which add mass or weight, but no electrical charge  Around the nucleus orbit the tiny electrons each with a charge of negative electricity, These are enough orbiting electrons to equal the positive charge of the nucleus, so the total atom is electrically neutral 

A good way to learn about them all is to study the Periodic Table, Here they are neatly arranged in lines and columns according to their family relationships  Each element is given a symbol of one or two letters and with it are its atomic number and mass number,

The atomic number is the number of protons in each atom of an element, Hydrogen is atomic number 1, mercury is atomic number 80, The mass is the total weight of the protons and neutrons in an atom.