Ann Potter, age 13, of Canada, for her question:

What is the molecular theory?

A theory is something to look over and think about, We may know enough about it to make it work for use But it remains a theory so long as parts of it are still unproved. The theory of molecules concerns the tiny particles of which the world is made. The ancient Greeks were the first to suggest that the world was made of tiny particles. They called these building blocks atoms.

The molecular theory is a development of this old idea. The atoms of which the world is made have been sorted and charted in modern times, There are less than 100 different ones. The problem is how can so few atoms form the thousands of different substances in the world, The theory of molecules is an explanation, Different atoms combine in bundles, The bundles are molecules different from any of the original atone, Late last century the binding power of molecules seemed to be electrical in nature.

Atoms themselves are made of electrical particles. Each atom has a certain number of protons charged with positive electricity.  It has the same number of electrons charged with negative electricity. The protons are knit together in the central nucleus, The electrons are arranged in shells around the nucleus. A healthy atom is balanced and electrically neutral.

Only the electrons seemed to take part in the formation of molecules from separate atoms, The little particles were given closer study, Atoms seemed able to swap electrons rind molecules were formed in the swapping, The shells of electrons are very orderly. An atom can hold up to two„ and no more. than twos electrons in its first inner shell, It can hold up to eight in its second shell. Atoms with three electrons must start a second shell. Atoms with 11 electrons must start a third.

Also, it seems that atoms with incomplete shells of electrons are not comfortable. The hydrogen atom has but one lone electron, It must lose or gain an electron before its shells are in order. The oxygen atom has a full inner shell of twos and six electrons in a second shell, It needs to gain two electrons to complete its second shell.

Suppose the oxygen atom grabbed an electron from each of two hydrogen atoms. That would solve the shell problem, But it would upset the electrical balance of each of the atoms. The oxygen atom would then have two' extra charges of negative electricity. Each hydrogen atom would be left with an extra charge of positive electricity. There is a way for these lopsided atoms to solve their problems,

Charges of positive and negative electricity act very like the poles of magnets, Two positive charges repel each other as do two negative charges, A positive charge and a negative charge attract each other, You’ve guessed it, The oxygen atom with two extra charges of negative electricity teams up with the two hydrogen atoms with an extra positive charge apiece. Together they form one molecule of water,

This is the most commonly accepted theory as to how atoms combine to form molecules, Electrons are swapped most likely to complete orderly shells, This creates electrical unbalance, Negative charges attract positive and the atoms are welded together in a new particle is a molecule.