The smallest piece of matter. An atom consists of a nucleus made up from equal numbers of nuetrons and protons, surround by an equal number of electrons. Each chemical element has varying numbers of protons, nuetrons and electrons. The heavier the element, the more protons, nutrons and electrons it has. Hydrogen, the lightest element, has one proton, one nuetron and one electron. Lead, which is much heavier, has eighty-two.