EXAMPLE 1 - Naming Polyatomic Ions:    Write names that correspond to the following formulas for polyatomic ions: (1) PO33- (with barium ions in glass) and (2) HSO4- (in perfumes).


  1. CrO42- is chromate ion. This is one of the polyatomic ions that you would need to memorize.

  2. PO33- is phosphite. PO43- is phosphate, and this ion has one less oxygen. 

  3. HSO4- is hydrogen sulfate. This could be called by its nonsystematic name, bisulfate, but it is preferable to use the systematic name, which shows that one H+ ion has been added to sulfate, SO42-.  

EXAMPLE 2 - Formulas for Polyatomic Ions:    Write formulas that correspond to the following names for polyatomic ions: (1) bromite ion, used in the production of cloth and (2) dihydrogen hypophosphite ion, used with manganese(II) ions as a food additive.


  1. Bromite ion is BrO2-. Bromate is BrO3-. Bromite has one less oxygen atom than bromate.

  2. Dihydrogen hypophosphite ion is H2PO2-. Hypophosphite has two less oxygen atoms than phosphate, PO43-. The dihydrogen part of the name indicates that two H+ ions have been added to hypophosphite, PO23-.  The two H+ ions neutralize two of the three minus charges, leaving -1.

Click here to see a sample exercise. 

Click here to convert oxyanion formulas to names. (Requires the Java Plug-in.)

Return to the Oxyanions Nomenclature Page.


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