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How do the prefixes hypo- and per- show the relative numbers of oxygen atoms in oxyanions?
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oxyacid
The structure of phosphorous acid, H3PO3.
In the nomenclature of oxyanions, which are polyatomic ions containing a central atom combined with varying numbers of oxygen atoms, the prefixes hypo- and per- are used when a series consists of more than two members to indicate the relative quantity of oxygen:
- hypo-: This prefix means "less than" and is used to designate the member of the series with the smallest number of oxygen atoms.
- per-: This prefix means "more than" and is used to designate the member of the series with the largest number of oxygen atoms.
For example, in the series of chlorine-containing oxyanions, the progression based on the number of oxygen atoms is as follows:
| Ion | Name |
| :--- | :--- |
| ClO⁻ | hypochlorite |
| ClO₂⁻ | chlorite |
| ClO₃⁻ | chlorate |
| ClO₄⁻ | perchlorate |
This system allows for the systematic naming of complex inorganic compounds by clearly distinguishing between different oxidation states of the central atom within the oxyanion structure.1