Dications

A dication is a positively charged ion with a +2 charge, also called a divalent cation. It forms when an atom loses two electrons, or when a neutral molecule becomes charged by removing two electrons. In formula notation, it is written as M2+.

Common dications include alkaline earth metal ions such as Mg2+, Ca2+, Sr2+, and Ba2+, as well as transition metal ions like Fe2+, Cu2+, Zn2+, and Co2+. Some elements can exist in different oxidation states, but +2 is among the most prevalent for many metals. In aqueous solution, dications are typically surrounded by water molecules, forming hydration shells that influence reactivity, solubility, and the formation of complexes.

Dications are central to salts and coordination chemistry. They pair with various counterions to form ionic compounds such as CaCl2 or MgSO4. In coordination complexes, dications can adopt diverse geometries, often octahedral for six-coordinate metals. Their redox chemistry can be important for catalysis and biological processes, although not all +2 ions are readily redox-active; for example, Fe2+ can be oxidized to Fe3+. In biology, calcium ions play key roles in signaling and bone structure, while magnesium ions are essential in enzymatic function and chlorophyll structure in plants.

See also: monocation, polycation, oxidation state, coordination chemistry.