IUPAC Nomenclature

Naming of Binary Compounds

Nomenclature refers to the system used for naming chemical compounds. The official system is provided by the IUPAC (International Union of Pure and Applied Chemistry). The name of a compound depends on the elements it contains and sometimes includes the oxidation number of the elements involved.

For binary compounds (compounds made of only two elements), the more electropositive element (the cation) is written first, followed by the more electronegative element (the anion), which ends in -ide.

Formula IUPAC Name
MgO Magnesium oxide
H2S Hydrogen sulphide
NH4Cl Ammonium chloride
NaH Sodium hydride

However, when both elements are non-metals, this rule does not apply. Examples include:

Naming of Radicals and Compounds with Variable Oxidation Numbers

Radicals are groups of atoms that carry an electric charge and are treated as single units when naming their compounds.

Radical IUPAC Name
NH4+ Ammonium ion
OH- Hydroxyl ion

For acid radicals, the oxidation number is shown using Roman numerals in brackets.

Formula IUPAC Name
NO2- Dioxonitrate(III) ion
NO3- Trioxonitrate(V) ion
CO32- Trioxocarbonate(IV) ion

Compounds that contain metals with multiple oxidation states also include the oxidation number in Roman numerals.

Formula IUPAC Name
FeO Iron(II) oxide
Cu2O Copper(I) oxide
MgCO3 Magnesium trioxocarbonate(IV)

Naming of Tertiary and Quaternary Compounds

These are compounds that contain more than two elements, such as oxo-acids, normal salts, and acid salts.

Examples of Oxo-Acids

Acid IUPAC Name
HNO3 Trioxonitrate(V) acid
H2SO4 Tetraoxosulphate(VI) acid
H3PO4 Tetraoxophosphate(V) acid

Examples of Normal Salts

Salt IUPAC Name
KNO3 Potassium trioxonitrate(V)
Na2SO4 Sodium tetraoxosulphate(VI)
CuCO3 Copper(II) trioxocarbonate(IV)

Naming of Compounds with Partially Replaced Cations

When a compound contains a hydrogen ion replacing part of a metal cation, it is named by listing:

  1. The metal (cation)
  2. The hydrogen
  3. The radical, with its oxidation number in Roman numerals
Formula IUPAC Name
NaHSO4 Sodium hydrogen tetraoxosulphate(VI)
KHSO3 Potassium hydrogen trioxosulphate(IV)