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Anions: Properties, Examples, and Their Role in Ionic Compounds

An overview of anions—negatively charged atoms or groups that gain electrons. Explore common examples (chloride, bromide, iodide), their properties, migration under voltage, and role in ionic solids and bonding.

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Definition

A anion is an atom or a cluster of atoms that has gained one or more electrons. With more electrons than protons, the species carries a negative electric charge. Such a charged particle is a type of ion.

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Common examples

Typical anions include chloride (Cl−), bromide (Br−) and iodide (I−). These three are monovalent anions: each can pair with a single hydrogen atom, a concept described by valency and the combining capacity with hydrogen.

Relation to other ions and solids

An ion is any charged atom or group of atoms. Anions are the negatively charged half of ionic species; the positively charged counterparts are called cations. In many ionic solids the anions are the larger constituents and the smaller cations occupy the spaces between them in the crystal lattice (crystals).

Movement and acid–base role

Under an applied voltage, anions migrate toward the anode (the electrode where oxidation takes place). Because anions commonly accept a proton (H+), they are often classified as a base in acid–base descriptions.

Simple element anions

According to the rules of chemical nomenclature, the name of such anions, which are mainly found in binary compounds, i.e. compounds consisting of only two elements, ends in -id. When naming these compounds, e.g. sodium chloride, the cationic part is always named first and the anionic part last.

Anions of the 7th main group

Anions of the 6th main group

Anions of the 5th main group

  • Nitride N3-
  • Phosphide P3-
  • Arsenide As3-
  • Antimonide Sb3-
  • Bismutide Bi3-

Anions of the 4th main group

  • Carbide C4-
  • Silicide Si4-
  • Germanid Ge4-

Anions of the 3rd main group

  • Boride Bx-

Anions of the 1st main group(*)

  • Hydride H-
  • Alkalis

Other element anions

  • Zintl Phases
  • Auride Au-
  • Platinide Pt2-

(*) No stable element anions are known from the second main group, only some intermetallic phases with more electropositive metals like the beryllides MxBey.

Complex anions

Oxygen-containing molecular anions

According to the rules of chemical nomenclature, the names of such anions usually end in -it or -at, although various prefixes such as hypo- (German unter-) or per- (German über-) may be added to distinguish the different oxidation states of the central atom.

Another way of designating anions of this type, although rather unusual, is according to the rules of complex chemistry, in which compounds with molecular anions containing oxygen are called oxo compounds and their oxygen atoms are treated as free ligands, so that, for example, sulfites are designated as trioxosulfates, sulfates as tetraoxosulfates, and so on.

8. main group

  • Hydrogen xenate HXeO4-
  • Xenat XeO42-
  • Perxenate XeO64-

7th main group

  • Hypochlorite ClO-
  • Chlorite ClO2-
  • Chlorate ClO3-
  • Perchlorate ClO4-
  • Hypobromite BrO-
  • Bromite BrO2-
  • Bromate BrO3-
  • Perbromate BrO4-
  • Hypoiodite IO-
  • Iodite IO2-
  • Iodate IO3-
  • Periodate IO4-

6. main group

  • Hydrogen sulphite HSO3-
  • Sulphite SO32-
  • Hydrogen sulphate HSO4-
  • Sulphate SO42-
  • Thiosulphate S2O32-
  • Dithionate S2O62-
  • Peroxodisulphate S2O82-
  • Selenite SeO32-
  • Selenate SeO42-
  • Tellurate TeO42-

5. main group

  • Hyponitrite NO-
  • Nitrite NO2-
  • Nitrate NO3-
  • Dihydrogen phosphate H2PO4-
  • Hydrogen phosphate HPO42-
  • Phosphate PO43-
  • Arsenate AsO43-
  • Antimonate SbO43-

4th main group

  • Hydrogen carbonate HCO3-
  • Carbonate CO32-
  • Silicate SiO44-
  • Germanate GeO44-
  • Stannate SnO32-

3rd main group

  • Borate BO33- or B4O72-
  • Aluminate

Subgroups

  • Chromate CrO42-
  • Dichromate Cr2O72-
  • Molybdate MoO42-
  • Niobate NbO3-
  • Permanganate MnO4-
  • Perrhenate ReO4-
  • Rhenat ReO42-
  • Tantalate TaO3-
  • Technetat TcO42-
  • Pertechnetate TcO4-
  • Titanate TiO3-
  • Wolframat WO42-
  • Zirconate

Other molecular anions

The rules of chemical nomenclature are inconsistent here - the name of some of these anions ends in -id, as with element anions, while the name of others ends in -at:

  • Cyanate OCN-
  • Thiocyanate SCN-
  • Cyanide CN-
  • Amide NH2-
  • Azide N3-

Halogen complexes

  • Tetrachloroaurate AuCl4-
  • Tetrachloroaluminate AlCl4-
  • Tetrafluoroborate BF4-
  • Hexachlorophosphate PCl6-
  • Hexachloroplatinate PtCl62-
  • Hexachloroosmat OsCl62-
  • Hexachloroiridate IrCl62-
  • Hexafluoroantimonate SbF6-
  • Hexafluoroarsenate AsF6-
  • Hexafluorophosphate PF6-
  • Hexafluorosilicate SiF62-
  • Hexafluorotitanate TiF62-
  • Hexafluorozirconate ZrF62-

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AlegsaOnline.com Anions: Properties, Examples, and Their Role in Ionic Compounds

URL: https://en.alegsaonline.com/art/4299

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