Themes > Science > Chemistry > Miscellenous > Help file Index > Naming rules > Binary compound names

For ionic compounds made up of an anion and a cation, naming is simple: simply attach the name of the anion to that of the cation. (See the rules for naming monatomic ions and polyatomic ions) For example, the compound NaNO3 starts with the name of the cation, sodium, then adds the name of the anion, nitrate, to form sodium nitrate.

For molecular compounds formed of two nonmetals, it is a bit tricker. The first word is the name of the first element, with a greek prefix to denote the number of atoms of that type. The second word is the root of the atom name, with the suffix -ide attached and a greek prefix again for the number of atoms. The prefixes are:

  • di: 2
  • tri: 3
  • tetra: 4
  • penta: 5
  • hexa: 6
  • hepta: 7
  • octo: 8

For example, the compound PCl5 would have the name phosphorus pentachloride. The first name is just the name of the element, the second is the root of the element name (chlor-) with -ide attached and the prefix to give the number. (5 = penta-)

Example: What are the names of the following compounds: CaSO4 and N2O4?

Solution: The first is an ionic compound made from a metal (calcium) and a polyatomic anion. Checking the polyatomic naming rules, the anion SO4-2 is the sulfate ion, so the entire molecule is named calcium sulfate.

The second is a compound made of two nonmetals. The first word is the name of the first atom (nitrogen) with the prefix di- attached to it to indicate that there are two of them. The latter is the root of the atom name: ox-, with the suffix -ide attached and the prefix tetra- to indicate there are four of them: dinitrogen tetraoxide


Information provided by: http://learn.chem.vt.edu