oxyanion
An oxyanion or oxoanion is a negatively charged polyatomic ion that contains oxide. Oxyanions can be viewed as the conjugate base of a corresponding oxyacid, although both components are not necessarily stable. Probably the best known oxyanion is DNA. The most extensive family of oxyanions are the polyoxomolybdates.
Some elements, Q, (Q = metals and nonmetals) form several oxyanions, QOxn- with different numbers of oxygen atoms, x, or different charges n. These oxyanions and their conjugate oxyacids are named according to the oxidation state of the non-oxygen atom, for example the four oxyanions of chlorine:
| Oxidation state | +1 | +3 | +5 | +7 |
|---|---|---|---|---|
| oxanion name | hypochlorite | chlorite | chlorate | perchlorate |
| formula | ClO− | ClO2− | ClO3− | ClO4− |
| structure |  |
 |
 |
 |
| Conjugate acid | Hypochlorous acid | Chlorous acid | Chloric acid | Perchloric acid |
| structure |  |
 |
 |
 |
For other oxyanions, the oxidation states may be different from these, but the order of the
prefixes and suffixes remains the same.
Oxyanions have some very important environmental roles. We can mention the case of prvalence of arsenic species in the arsenic
affected areas in the form of oxyanions. Surface water usually exhibit oxidizing conditions and under such condition, arsenic
species tend to prevail in pentavalent arsenic form, mainly in its oxyanionic forms H2AsO4-, and
HAsO42-.
Well known oxyanions
- With terminal oxide groups:
- With both bridging and terminal oxide groups:
- dichromate
- pyrophosphate
- polyoxometalates such as phosphomolybdate and phosphotungstate
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