A positively or negatively charged atom is called an ion.
Atoms can gain or lose electrons. The loss or gain of electrons to form a charged atom is called ionisation.When an atom loses an electron it becomes a positively charged ion or cation. This is because there are now more protons than electrons and the charges are no longer balanced.When an atom gains an electron it becomes negatively charged. A negatively charged ion is called an anion.Metals tend to lose electrons and non-metals tend to gain electrons.