Letters of a Radio-Engineer to His Son
No matter what kind of atom we are considering there is always in it just as many electrons as protons. For example, the iron atom is formed by a nucleus and twenty-six electrons playing around it. The copper atom has twenty-nine electrons as tiny planets to its nucleus. What does that mean about its nucleus? That there are twenty-nine more protons in the nucleus than there are electrons. Silver has even more planetary electrons, for it has 47. Radium has 88 and the heaviest atom of all, that of uranium, has 92.
We might use numbers for the different kinds of atoms instead of names if we wanted to do so. We could describe any kind of atom