Äons

Íons are atoms or molecules that carry a net electric charge as a result of electron loss or gain. The charged species arise when atoms or groups acquire or shed electrons, producing positive charges (cations) or negative charges (anions). Polyatomic ions are ions composed of multiple atoms bonded together with an overall charge, such as sulfate (SO4 2−) or ammonium (NH4+).

Formation and charge: Ionization can occur through chemical reactions, redox processes, or in ionized gases and solutions. Losing electrons yields cations; gaining electrons yields anions. Ion charge is indicated by a superscript, for example Na+ or SO4 2−.

Physical properties: Ions interact via electrostatic forces; ionic bonds form between oppositely charged ions in ionic compounds. In solids, ions arrange in crystal lattices; in liquids, they can move and conduct electricity when mobile. In water or other solvents, ions are surrounded by solvent molecules in solvation shells (hydration in water).

Occurrence and roles: Ions are ubiquitous in chemistry, geology, and biology. Salt minerals consist of alternating cations and anions. In living organisms, ions such as Na+, K+, Ca2+, and Cl− are essential for nerve signaling, osmoregulation, and muscle contraction. Technological applications include batteries, electroplating, and electrolysis.

Notation and measurement: Ions are identified by charge and composition; analytical techniques include mass spectrometry and ion chromatography. The concept of ions underpins pH, acid–base chemistry, and redox processes.