What Is the Difference Between a Cation and an Anion?

Cation vs. Anion

A cation is an atom or molecule with a net positive charge, while an anion is an atom or molecule with a net negative electrical charge. jack0m / Getty Images

Cations and anions are both ions. The difference between a cation and an anion is the net electrical charge of the ion.

Ions are atoms or molecules which have gained or lost one or more valence electrons giving the ion a net positive or negative charge.

Cations are ions with a net positive charge.

Cation Examples: Silver: Ag+, hydronium: H3O+, and ammonium: NH4+

Anions are ions with a net negative charge.

Anion Examples: hydroxide anion: OH-, oxide anion: O2-, and sulfate anion: SO42-

Sometimes you can predict whether an atom will form a cation or an anion based on its position on the periodic table. Alkali metals and alkaline earths always form cations. Halogens always form anions. Most other nonmetals typically form anions (e.g., oxygen, nitrogen, sulfur), while most metals form cations (e.g., iron, gold, mercury).