The atomic number is the number of protons in the nucleus of an atom. The number of protons define the identity of an element (i.e., an element with 8 protons is a carbon atom, no matter how many neutrons may be present). If an atom loses or gains electrons, it will become a positively or negatively charged particle, called an ion. The loss of one or more electrons results in more protons than electrons and an overall positively charged ion, called a cation.