Key learning points

1. Atoms are more stable when they have a full outer shell.
2. Metal atoms become more stable when they lose the electron(s) in their outer shell, and become positive ions (cations).
3. Non–metal atoms become more stable when they gain electrons to fill their outer shell and become negative ions (anions).
4. Ions form through the loss or gain of electrons.
5. Standard ion notation uses superscript charge values where the charge follows the number (e.g. 2+, not +2).

Keywords

• Ion - An atom or molecule that has lost or gained one or more electrons so has a charge.

• Cation - A positively charged ion.

• Anion - A negatively charged ion.

• Dot–and–cross diagram - Used to show how chemical bonds are formed between atoms – the electrons from one atom are shown as dots and the electrons from the other atom are shown as crosses.

Common misconception