Matter is made up of . Each atom consists of a surrounded by orbiting electrons. The electrons have a charge. In the nucleus there are and neutrons. The protons have a positive charge, while the have no charge.

In the neutral atom the number of protons is the as the number of electrons. Therefore the charges balance out.

If we remove an electron, the atom becaomes positively charged. It is a positive . If we add an electron, we get a ion.

Isotopes have the same number of protons but different numbers of . They have the same chemical properties as the original element. Some isotopes are instable, therefore are .

If we change the number of protons, we change the .