Polyatomic Ion Naming Patterns
Common oxyanion naming relationships, with the halogen oxygen-count ladder and explicitly identified exceptions. This table explains names; it is not an exhaustive catalogue of all oxyanions.
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 same-charge oxygen-count ladder applies to the halogen examples. Other families and exceptional names require the qualifications below.
| 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 | Outside this naming ladder | NO3- nitrate | NO2- nitrite | N2O22- hyponitrite (exception) |
| Sulfur | Outside this naming ladder | SO42- sulfate | SO32- sulfite | Outside this naming ladder |
| Phosphorus | Outside this naming ladder | PO43- phosphate | HPO32- aqueous phosphite; PO33- formal phosphite | H2PO2- hypophosphite (exception) |
| Carbon | Outside this naming ladder | CO32- carbonate | Outside this naming ladder | Outside this naming ladder |
| Manganese | MnO4- permanganate | MnO42- manganate | Outside this naming ladder | Outside this naming ladder |
| Chromium | Outside this naming ladder | CrO42- chromate | Outside this naming ladder | Outside this naming ladder |
Important Notes
- For the halogen ladder shown, per-...-ate has one more oxygen than -ate, -ite has one fewer than -ate, and hypo-...-ite has two fewer than -ate. Charge stays the same within these illustrated ladders. IO4- is metaperiodate; other periodate forms also exist.
- Outside this naming ladder means the simple oxygen-count rule does not supply a corresponding entry here. It does not mean an ion is unknown or nonexistent. This is a naming reference for selected common families, not a complete inventory of chemistry.
- Nitrate and nitrite differ by one oxygen at the same charge. Hyponitrite, N2O22-, exists but contains two nitrogen atoms and is an exception to the single-nitrogen ladder. Peroxynitrate, NO4-, also exists; its peroxo group requires a different naming relationship.
- Sulfate and sulfite differ by one oxygen at the same charge. Peroxodisulfate, S2O82-, and peroxomonosulfate, HSO5-, are known peroxo species outside the simple sulfate/sulfite ladder.
- Aqueous phosphite species retain hydrogen bonded to phosphorus: HPO32- (hydrogenphosphite) and H2PO3- (dihydrogenphosphite). Hypophosphite is H2PO2-. Their charges and hydrogen content differ from phosphate, so do not infer their formulas from a same-charge oxygen-count rule. PO33- is also recorded as phosphite(3−); distinguish that formal ion from the usual hydrogen-containing aqueous species.
- Permanganate, MnO4-, and manganate, MnO42-, have the same oxygen count and different charges. The per- prefix in this pair is an exception to the halogen ladder.
- Carbonate and chromate are selected -ate names here. The table does not infer matching per-, -ite, or hypo- forms from those names alone.
- Adding a proton to an oxyanion makes its charge one unit less negative and adds hydrogen to the name: SO42- sulfate → HSO4- hydrogen sulfate (bisulfate).
- The prefix thio- denotes replacement of oxygen by sulfur: SO42- sulfate → S2O32- thiosulfate.
- For conventional oxyacid names, -ate corresponds to -ic acid and -ite to -ous acid: sulfate/sulfuric acid and sulfite/sulfurous acid.
Verification references: OpenStax Chemistry 2e, Section 2.6 (oxyanion -ate/-ite and per-/hypo- naming rules); ChEBI entries for hydrogenphosphite, hyponitrite and phosphinate (hypophosphite); PubChem Peroxynitrate, CID 5460620; ChEBI phosphite(3−), CHEBI:45064.