Chemical Nomenclature Cheat Sheet
Naming ionic and molecular compounds, acids, and hydrates, plus the common polyatomic ions.
Keep going with the free Chemical Nomenclature study guide → (graded practice with a subscription).
Chemical Nomenclature
Naming ionic and molecular compounds, acids, and hydrates, plus the common polyatomic ions.
Ionic or molecular?
CORE RULEMetal + nonmetal (or polyatomic ion): ionic. Only nonmetals: usually covalent, and many are molecular (SiO₂ is network-covalent). Heuristic, not a law: NH₄Cl is ionic with no metal.
Common ion charges
REFERENCEGroup 1 → +1 · Group 2 → +2 · Al → +3 · N, P → −3 · O, S → −2 · F, Cl, Br, I → −1. Introductory patterns, not universal oxidation states.
Common polyatomic ions
REFERENCE| Name | Formula | Charge |
|---|---|---|
| ammonium | NH₄⁺ | +1 |
| hydroxide | OH⁻ | −1 |
| nitrate | NO₃⁻ | −1 |
| nitrite | NO₂⁻ | −1 |
| sulfate | SO₄²⁻ | −2 |
| sulfite | SO₃²⁻ | −2 |
| phosphate | PO₄³⁻ | −3 |
| phosphite | PO₃³⁻ | −3 |
| carbonate | CO₃²⁻ | −2 |
| hydrogen carbonate (bicarbonate) | HCO₃⁻ | −1 |
| acetate | CH₃COO⁻ | −1 |
| permanganate | MnO₄⁻ | −1 |
| chromate | CrO₄²⁻ | −2 |
| dichromate | Cr₂O₇²⁻ | −2 |
| cyanide | CN⁻ | −1 |
| hydrogen sulfate | HSO₄⁻ | −1 |
| hydrogen phosphate | HPO₄²⁻ | −2 |
| dihydrogen phosphate | H₂PO₄⁻ | −1 |
Oxoanion series (most O to least O)
REFERENCEper-…-ate (most O) › -ate › -ite › hypo-…-ite (least O). Chlorine: ClO₄⁻ perchlorate, ClO₃⁻ chlorate, ClO₂⁻ chlorite, ClO⁻ hypochlorite.
Naming ionic compounds
METHODBinary (two elements): cation name (unchanged) + anion root + -ide. Never use Greek prefixes on ionic names.
With a polyatomic ion, use its name from the table unchanged (Na₂SO₄ = sodium sulfate; NH₄NO₃ = ammonium nitrate).
Balance charge: pick coprime subscripts x, y so x·|cation| = y·|anion|, then reduce to lowest terms. Wrap a polyatomic ion in parentheses when its subscript is > 1.
Formula: cation first, then anion; integer subscripts; reduce to lowest terms (CaO, not Ca₂O₂).
Metals with more than one charge: Stock system
CORE RULEAppend a Roman numeral in parentheses (the charge) right after the metal name, no space: Fe²⁺ iron(II), Fe³⁺ iron(III), Cu⁺ copper(I), Cu²⁺ copper(II).
Naming molecular (covalent) compounds
CORE RULEName = prefix + first element + prefix + second-element root + -ide. Drop mono- on the first element. Elide vowel clashes: monoxide, tetroxide, pentoxide.
Greek prefixes
REFERENCEGreek numerical prefixes: mono- (1), di- (2), tri- (3), tetra- (4), penta- (5), hexa- (6), hepta- (7), octa- (8), nona- (9), deca- (10). Additional for hydrates: dodeca- (12).
Naming acids (aqueous)
CORE RULENo oxygen (hydroacid): hydro-<root>-ic acid (HCl(aq) → hydrochloric acid). From an -ate anion: -ic acid (NO₃⁻ → HNO₃ nitric acid). From an -ite anion: -ous acid (NO₂⁻ → HNO₂ nitrous acid). Extend with per-…-ic and hypo-…-ous.
Hydrates
CORE RULEFormula: <anhydrous salt> · n H₂O. Name: <salt name> <Greek-prefix>hydrate, where the prefix is n (CuSO₄·5H₂O = copper(II) sulfate pentahydrate).
Common mistakes
WATCH OUTCharges must balance (NaCl₂ is net −1, invalid). No Greek prefixes on ionic names. Stock uses Roman numerals in parentheses, not iron 3 or iron(3). Never use hydro- on an oxyacid.