Atoms are the smallest bits of ordinary matter and are made from particles called protons (which carry a positive electrical charge), neutrons (which carry no electrical charge) and electrons (which carry a negative electrical charge). The protons and neutrons cluster together in the central part of the atom, called the nucleus, and the electrons 'orbit' the nucleus. A particular atom will have the same number of protons and electrons and most atoms have at least as many neutrons as protons.