cation

A cation is an ion with a positive electric charge. Cations form when atoms or molecules lose electrons; metal atoms commonly become cations by oxidation, while certain polyatomic species such as ammonium (NH4+) and hydronium (H3O+) are also cations in solution. By convention, cations are attracted to the cathode during electrolysis.

Charge and examples: Cations are classified by their charge: monovalent (+1) such as H+, Li+, Na+, K+, Ag+; divalent (+2) such as Mg2+, Ca2+, Zn2+; trivalent (+3) such as Al3+. Multivalent cations exist in many transition metals (Fe2+, Fe3+, Cu2+, Mn2+), and others. In aqueous solution, cations are typically hydrated, i.e., surrounded by water molecules, which affects reactivity and mobility.

Occurrence and roles: Cations balance electroneutrality with anions in salts and minerals. They are central in biology (e.g., Na+, K+, Ca2+ ions regulate nerves, muscles, and enzymes). In chemistry, they participate in complex formation, catalysis, and electrochemical processes.

Etymology and naming: The term cation was introduced in the 19th century by Faraday to denote ions that migrate toward the cathode; 'cation' and 'anion' reflect the directions relative to the electrodes.