At the centre of every atom is a tiny nucleus. The nucleus is made of two kinds of particle, protons and neutrons. A proton has a relative charge of +1. A neutron is neutral, so it has no charge. Because the nucleus contains protons and neutral neutrons, the nucleus always has an overall positive charge.
The size of the positive charge depends on how many protons there are. A nucleus with 6 protons has a relative charge of +6, and a nucleus with 8 protons has a relative charge of +8. Every atom of one element has the same number of protons, so the nucleus of each element has its own characteristic positive charge. The number of protons is what decides which element an atom is: 6 protons is always carbon and 8 protons is always oxygen.
The electrons move around outside the nucleus and each has a relative charge of -1. An atom has no overall charge because the number of electrons equals the number of protons.
