ion

An ion is a particle like an atom that has lost or gained electrons.

Atoms have a centre called a nucleus, which contains protons and neutrons. Protons have a positive charge, neutrons have no charge, and electrons have a negative charge. Normally, atoms have the same number of protons and electrons, so they have no overall charge. But if an atom loses or gains electrons, it will have an overall charge. Atoms that lose electrons become positively charged ions, called cations. Atoms that gain electrons become negatively charged ions, called anions.

For example, salt is made up of sodium ions (Na+) and chlorine ions (Cl-). Sodium ions have lost one electron, so they have a positive charge. Chlorine ions have gained one electron, so they have a negative charge. When sodium and chlorine ions come together, they form a neutral molecule of salt.

The salt solution is made up of ions.