Chemistry terminology

International standards and resources

The most comprehensive source for information on chemistry terminology is the International Union of Pure and Applied Chemistry (IUPAC).

The names of chemical compounds are set by complex rules established by IUPAC; the International Union of Biochemistry and Molecular Biology (IUBMB); and the Committee on Nomenclature, Terminology, and Symbols of the American Chemical Society.

IUPAC’s rules are contained in a series of ‘colour books’:

  • Blue Book – organic chemistry
  • Red Book – inorganic chemistry
  • Green Book (in association with the International Union of Pure and Applied Physics) – use of symbols for physical quantities (see also Physics)
  • Gold Book – definitions of technical terms used in chemistry
  • White Book (in association with IUBMB) – biochemistry (see also Cell biology)
  • Orange Book – analytical terminology (see also Analytical methods)
  • Purple Book – macromolecular chemistry
  • Silver Book – clinical chemistry (see also Health and medicine).

The Chemical Abstracts Service (CAS), a division of the American Chemical Society, maintains a database of all chemical substance information. All chemical substances in the database are given a unique identifying number (CAS Registry Number), which allows a substance to be identified when it has a number of possible systematic, generic, proprietary or trivial names.

The Merck Index is another useful reference for chemical names (but beware of American spellings).

The ACS style guide: effective communication of scientific information (3rd edition) (American Chemical Society) is a useful resource for chemistry terms.

Australian conventions and resources

Chemists in Australia follow the international conventions of IUPAC. Where there is a choice between American and British spelling, Australian style is to use British spelling (but see Spelling in chemistry for some exceptions).

Spelling in chemistry

Where a choice exists between British and American spelling, use the spelling preferred by IUPAC:

aluminium  not   aluminum    

sulfur   not   sulphur    

caesium   not   cesium

Watch out for different spellings for elements and their different valencies in compounds:

phosphorus [for elemental phosphorus]

phosphoric [for phosphorus compounds with a valency of 5; eg phosphoric acid, orthophosphonic acid]

phosphorous [for reduced phosphorus compounds with a valency of 3; eg phosphorous acid – also known as phosphonic acid; hypophosphorous acid]

sulfur [for elemental sulfur]

sulfurous [for sulfur compounds with a valency of 4; eg sulfurous acid]

sulfuric [for sulfur compounds with a valency of 6; eg sulfuric acid]

sulfonate, sulfate, sulfite … [and ALL other derivatives, including endosulfan and similar terms]

Note: IUPAC has standardised the spelling of sulfur (not sulphur). The only place that the ph spelling should be retained is in formal names (such as bird or insect names):

sulphur-crested cockatoo   not   sulfur-crested cockatoo    

bordered sulphur   not   bordered sulfur

Did you know?

The last word on sulfur!
The spelling sulfur is often thought of as American and sulphur as British. However, this is incorrect, and sulfur is the standard spelling recommended by IUPAC, and used by chemists and other science disciplines worldwide. Australian authors outside science often mistakenly think that the choice of spelling is still optional and argue for sulphur because of the association with British spelling. But, in addition to the international standardisation of the spelling by IUPAC, sulfur is the sounder spelling, originating from Latin (not Greek). The word’s earliest spellings were sulfur and sulpur, and the introduction of ph into the spelling is a scholarly mistake.

(Adapted from Pam Peters’s Cambridge guide to Australian English usage)

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