diiones

Diione is a term sometimes used to refer to a chemical species that carries two elementary charges. In standard chemical terminology, such species are usually called dianions (2− charge) or dications (2+ charge). More generally, ions with a double charge are described as divalent ions. The term diione is not widely used in formal literature, but it may appear in introductory discussions or as a shorthand in some contexts.

Dications are positively charged ions formed when an atom loses two electrons. Common examples include Ca2+, Mg2+, Fe2+, and Zn2+. In solid salts, these cations balance with various anions to form electrically neutral compounds. Dications play important roles in coordination chemistry, catalysis, and materials science, where their charge density influences bonding, geometry, and reactivity.

Dianions are negatively charged ions with a 2− charge. Well-known examples are carbonate (CO3^2−), sulfate (SO4^2−), oxalate (C2O4^2−), chromate (CrO4^2−), and dichromate (Cr2O7^2−). Dianions are common in inorganic salts and in solution, where their high negative charge affects solubility, hydration, and interactions with counterions. In aqueous solutions, dianions are often stabilized by hydration shells and electrostatic pairing with cations; in nonaqueous media, dianions can be stabilized by suitable solvents and counterions.

Diions are encountered across chemistry, including electrochemistry, mineralogy, and biological systems, wherever species bearing two units of charge influence structure and reactivity. See also: divalent ion, monovalent ion.