text: There are several patterns that can be used for learning the nomenclature of polyatomic anions. First, when the prefix bi is added to a name, a hydrogen is added to the ions formula and its charge is increased by 1, the latter being a consequence of the hydrogen ions +1 charge. An alternative to the bi- prefix is to use the word hydrogen in its place: the anion derived from . For example, let us consider carbonate() ion.
  It is either called as bicarbonate or hydrogen carbonate.
  This process is called protonation.
  Most of the common polyatomic anions are oxyanions, conjugate bases of oxyacids (acids derived from the oxides of non-metallic elements). For example, the sulfate anion, , is derived from , which can be regarded as  + .
  The second rule is based on the oxidation state of the central atom in the ion, which in practice is often (but not always) directly related to the number of oxygen atoms in the ion, following the pattern shown below. The following table shows the chlorine oxyanion family:
  As the number of oxygen atoms bound to chlorine increases, the chlorines oxidation number becomes more positive. This gives rise to the following common pattern: first, the -ate ion is considered to be the base name; adding a per- prefix adds an oxygen, while changing the -ate suffix to -ite will reduce the oxygens by one, and keeping the suffix -ite and adding the prefix hypo- reduces the number of oxygens by one more, all without changing the charge. The naming pattern follows within many different oxyanion series based on a standard root for that particular series. The -ite has one less oxygen than the -ate, but different -ate' anions might have different numbers of oxygen atoms.
  These rules do not work with all polyatomic anions, but they do apply to several of the more common ones. The following table shows how these prefixes are used for some of these common anion groups.
  Some oxo-anions can dimerize with loss of an oxygen atom. The prefix pyro is used, as the reaction that forms these types of chemicals often involves heating to form these types of structures. The prefix pyro is also denoted by the prefix di- . For example, dichromate ion is a dimer.