aniooni

Anion, in chemistry, denotes a negatively charged ion. Anions form when atoms or molecules gain one or more electrons, and they commonly pair with positively charged cations in salts. They are distinguished from cations, which carry a positive charge.

Monatomic anions include halide ions such as chloride (Cl−), fluoride (F−), and bromide (Br−), as well as oxide (O2−), nitride (N3−), and sulfide (S2−). Polyatomic anions include nitrate (NO3−), nitrite (NO2−), carbonate (CO32−), sulfate (SO42−), phosphate (PO43−), and hydroxide (OH−). Anions can arise from acid–base reactions, dissolution of salts, or redox processes that remove protons or add electrons to a species.

Naming follows established rules: many inorganic anions end with -ide for simple ions (chloride, oxide), while oxyanions use -ate or -ite endings (nitrate vs nitrite, sulfate vs sulfite). Per-, hypo-, and other prefixes indicate higher or lower oxygen content (e.g., perchlorate, hypochlorite).

Occurrences and roles: anions are central to the composition of minerals, salts, and many biological systems. Chloride maintains electrical neutrality and fluid balance in organisms; phosphate groups form part of nucleic acids and energy carriers. Anions influence solution conductivity, acid–base chemistry, and redox behavior in chemical processes.

Detection and analysis: common methods include ion chromatography, electrophoresis, and mass spectrometry. In solution, the behavior of anions depends on charge density, size, hydration, and the surrounding cations.