Sometimes they do get very close together. I can tell you how if you will imagine four small boys playing tag. Suppose Tom and Dick don't like to play with each other and run away from each other if they can. Now suppose that Bill and Sam won't play with each other if they can help it but that either of them will play with Tom or Dick whenever there is a chance. Now suppose Tom and Bill see each other; they start running toward each other to get up some sort of a game. But Sam sees Tom at the same time, so he starts running to join him even though Bill is going to be there too. Meanwhile Dick sees Bill and Sam running along and since they are his natural playmates he follows them. In a minute they are all together, and playing a great game; although some of the boys don't like to play together. Whenever there is a group of protons and electrons playing together we have what we call an "atom." There are about ninety different games which electrons and protons can play, that is ninety different kinds of atoms. These games differ in the number of electrons and protons who play and in the way they arrange themselves. Larger games can be formed if a number of atoms join together. Then there is a "molecule." Of molecules there are as many kinds as there are different substances in the world. It takes a lot of molecules together to form something big enough to see, for even the largest molecule, that of starch, is much too small to be seen by itself with the best possible microscope. What sort of a molecule is formed will depend upon how many and what kinds of atoms group together to play the larger game. Whenever there is a big game it doesn't mean that the little atomic groups which enter into it are all changed around. They keep together like a troop of boy scouts in a grand picnic in which lots of troops are present. At any rate they keep together enough so that we can still call them a group, that is an atom, even though they do adapt their game somewhat so as to fit in with other groups--that is with other atoms. What will the kind of atom depend upon? It will depend upon how many electrons and protons are grouped together in it to play their little game. How any atom behaves so far as associating with other groups or atoms will depend upon what sort of a game its own electrons and protons are playing. Now the simplest kind of a game that can be played, and the one with the smallest number of electrons and protons, is that played by a single proton and a single electron. I don't know just how it is played but I should guess that they sort of chase each other around in circles. At any rate I do know that the atom called "hydrogen" is formed by just one proton and one electron. Suppose they were magnified until they were as large as the moon and the earth. Then they would be just about as far apart but the smaller one would be the proton.