Polyatomic Ion Naming Patterns
The systematic per-, -ate, -ite, hypo- naming pattern for oxyanions, organized by element series. Master this pattern to name the common oxyanion families from their formulas.
Naming or writing an oxyanion within a family using the per-, -ate, -ite, hypo- pattern (clearest for the halogen oxyanions: ClO4-, ClO3-, ClO2-, ClO-).
Within a family the -ate ion is the base: per- adds one O, -ite drops one O, hypo-___-ite drops two.
This is a common naming convention, not a universal rule: not every named series runs the full ladder or keeps a constant charge (e.g. permanganate MnO4- vs manganate MnO42-).
Oxyanion Naming: per-, -ate, -ite, hypo-
The per-, -ate, -ite, hypo- ladder applies within a family of related oxyanions; a few common ions are exceptions.
| Chlorine | ClO4- perchlorate | ClO3- chlorate | ClO2- chlorite | ClO- hypochlorite |
| Bromine | BrO4- perbromate | BrO3- bromate | BrO2- bromite | BrO- hypobromite |
| Iodine | IO4- periodate | IO3- iodate | IO2- iodite | IO- hypoiodite |
| Nitrogen | — | NO3- nitrate | NO2- nitrite | — |
| Sulfur | — | SO42- sulfate | SO32- sulfite | — |
| Phosphorus | — | PO43- phosphate | PO33- phosphite | — |
| Carbon | — | CO32- carbonate | — | — |
| Manganese | MnO4- permanganate | MnO42- manganate | — | — |
| Chromium | — | CrO42- chromate | — | — |
Important Notes
- The -ate form is the base (most common) ion in each series. All other names derive from it.
- per-___-ate = one more oxygen than -ate. Same charge as -ate.
- -ite = one fewer oxygen than -ate. Same charge as -ate.
- hypo-___-ite = one fewer oxygen than -ite (two fewer than -ate). Same charge as -ate.
- The charge stays the same across the entire series for a given element; only the number of oxygen atoms changes.
- Not all elements have all four forms. Nitrogen and sulfur series have only -ate and -ite forms in common use.
- Adding hydrogen (H) to an oxyanion reduces the charge by 1 and adds the prefix "hydrogen": SO42- (sulfate) → HSO4- (hydrogen sulfate or bisulfate).
- The prefix "thio-" replaces one oxygen with sulfur: SO42- (sulfate) → S2O32- (thiosulfate).
- The matching acids follow the same ladder: -ate becomes -ic acid (SO42- sulfate, H2SO4 sulfuric acid) and -ite becomes -ous acid (SO32- sulfite, H2SO3 sulfurous acid).
Verification references: OpenStax Chemistry 2e, Section 2.6 (oxyanion -ate/-ite and per-/hypo- naming rules).