What is the term for a positively charged ion?

The term for a positively charged ion is a cation. A cation has fewer electrons than protons, giving it a net positive electrical charge. Sodium ion, written Na⁺, is a familiar example.

Atoms often become cations by losing one or more electrons. Metals tend to do this because their outer electrons are relatively easy to remove. Magnesium commonly loses two electrons to form Mg²⁺, while aluminium can lose three to form Al³⁺. The number of lost electrons determines the ion's charge.

The opposite type of ion is an anion, which carries a negative charge because it has gained electrons. In table salt, positively charged sodium cations and negatively charged chloride anions attract each other, forming an ionic compound. Cations and anions can be single atoms or parts of larger charged groups.

A cation is not the same as a radical, isotope, or any atom with a changed nucleus. An isotope differs in neutron number, while ionisation changes the number of electrons. The word cation comes from the Greek idea of moving downward toward a cathode during electrolysis, a term introduced by Michael Faraday in the 19th century.