Polyatomic

Polyatomic is a term used in chemistry to describe a species that contains more than two atoms held together by covalent bonds. In common usage, diatomic molecules such as O2 or N2 are not considered polyatomic. Polyatomic species can be neutral molecules or charged ions.

Examples of neutral polyatomic molecules include water (H2O), ammonia (NH3), methane (CH4), and sulfur hexafluoride (SF6). These arise from sharing electrons among three or more atoms, forming stable structures with characteristic shapes determined by the arrangement of covalent bonds and lone pairs.

Polyatomic ions are charged species composed of two or more atoms whose bonds hold an overall charge. Well-known polyatomic ions include ammonium (NH4+), hydroxide (OH−), carbonate (CO3^2−), nitrate (NO3−), sulfate (SO4^2−), and phosphate (PO4^3−). In salts, they combine with counterions to balance charge.

Bonding in polyatomic species often involves resonance, which distributes charge over several atoms and stabilizes the structure. Geometries vary widely—from linear and trigonal planar to tetrahedral and octahedral—reflecting the number of bonds and lone pairs around central atoms.

Polyatomic species are central to many aspects of chemistry and biology, including acid-base chemistry, precipitation reactions, and catalysis. They also play key roles in living systems (phosphate groups in ATP and nucleic acids) and in environmental processes (nitrates in soils, carbonates in rocks).