Isopolyanions derived by the condensation of molecules of the same acid and containing the central element in the oxidation state corresponding to its group number [e.g., P(V), Mo(VI), are named by indicating the number of atoms of the central element with Greek numeral prefixes.

Examples :
                    S₂O₇^2-                 disulphate                            Mo₇O₂₄^6-        heptamolybdate
                    P₃O₁₀^5-              triphosphate                        Na₂B₄O₇          disodium tetraborate
                    Cr₄O₁₃^2-             tetrachromate

Cyclic and straight-chain molecular arrangement can be distinguished by means of the prefixes cyclo and catena, respectively.

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