Anionic

Anionic is an adjective used in chemistry to describe species that carry a negative electrical charge. Anions are negatively charged ions formed when atoms or molecules gain electrons or lose proton equivalents. The term is used in contrast to cationic (positive charge) and neutral.

In solution, anions are solvated by water and migrate under electric fields; their mobility depends on charge and size. Common inorganic anions include chloride (Cl-), hydroxide (OH-), nitrate (NO3-), sulfate (SO4^2-), carbonate (CO3^2-), and phosphate (PO4^3-). Many organic anions arise from deprotonation of acids, such as acetate (C2H3O2-). Anions can also form complexes with metals, influencing reactivity and conductivity.

Anions play key roles in many contexts. Anionic surfactants are widely used in detergents for their surface-active properties. Anionic exchange resins remove anions from solutions in water treatment and chemical separations. In biology, biomolecules can possess anionic character at physiological pH due to acidic amino acid residues or the phosphate backbone of nucleic acids, affecting interactions and stability.

Naming conventions: monatomic anions typically end with -ide, e.g., chloride, oxide. Polyatomic anions use -ate or -ite endings, e.g., sulfate (SO4^2-), sulfite (SO3^2-). Some common ions have historical or widely accepted names, such as hydroxide (OH-) and nitrate (NO3-).