An atom consist of a central portion called the nucleus, and one or more electrons. that constantly move around the nucleus. The nucleus contains one or more relatively large particles, protons and usually neutrons. Protons and neutrons are about equal in weight, but they are otherwise different. Electrons are so small they at they have almost no weight, carry a single negative electrical charge e- each proton carries a single, positive electrical charge p+ Neutrons are uncharged and thus are electrically neutral. the neucleus contains protons, so this part of an atom is always positively charged. However the number of electrons outside the nucleus equals the number of protons , so a complete atom is said to have no net charge and is thus electrically neutral.