Anion

Anions are atoms or radicals (groups of atoms), that have gained electrons. Since they now have more electrons than protons, anions have a negative charge. For example, chloride ions Cl- , bromide Br- , iodide I-. These are monovalent anions, meaning they have a valency (combining capacity) with only one ion of hydrogen. Similarly there are bivalent anions, etc.

An ion is an atom (or group of atoms) with an electrical charge. Anions are one of the two types of ions. The other type is called a cation, having a positive charge. In many crystals the anions are bigger; the little cations fit into the spaces between them.

Anions are termed so because they are attracted towards the anode (the positive electrode). All anions tend to accept a proton H+ thus they are categorised as base.

Anion Media

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  Electron transfer from a neutral lithium (Li) atom on the left to a neutral fluorine (F) atom on the right would give a Li⁺ and F⁻ ions.

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  Schematic of an ion chamber, showing drift of ions. Electrons drift faster than positive ions due to their much smaller mass.

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  Avalanche effect between two electrodes. The original ionization event liberates one electron, and each subsequent collision liberates a further electron, so two electrons emerge from each collision: the ionizing electron and the liberated electron.

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  Equivalent notations for an iron atom (Fe) that lost two electrons, referred to as ferrous.

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  Mixed Roman numerals and charge notations for the uranyl ion. The oxidation state of the metal is shown as superscripted Roman numerals, whereas the charge of the entire complex is shown by the angle symbol together with the magnitude and sign of the net charge.

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  An electrostatic potential map of the nitrate ion (2NO−
  3). The 3-dimensional shell represents a single arbitrary isopotential.