kation

A cation is a positively charged ion formed when an atom or molecule loses one or more electrons. Cations are attracted to the cathode in electrochemical processes and tend to migrate toward the negative electrode in electrical fields. In solution, cations are the positively charged species corresponding to the anions, the latter carrying a negative charge.

Cations can be monatomic, such as Na+, K+, and Ca2+, or polyatomic, such as ammonium (NH4+) and hydronium (H3O+). They arise from various processes, including metal atoms becoming positively charged in salts, acids donating protons to form H+ or H3O+, and other ionization or protonation reactions. The total charge of a cation is equal to the deficiency of electrons relative to its nucleus.

Nomenclature distinguishes simple metal cations by their charge, often written with parentheses (for example, iron(III) for Fe3+). Polyatomic cations have fixed common names (ammonium, hydronium) or systematic names when needed. Cations are contrasted with anions, which are negatively charged ions.

In aqueous solutions, cations are typically surrounded by a hydration shell and their mobility depends on size and charge density. They play essential roles in chemistry, biology, and industry, including electrolyte function in solutions, participation in redox reactions, and formation of salts that affect water hardness and soil chemistry. Examples of common ions include Na+, K+, Ca2+, NH4+, and H3O+.