In my notes, I've used phrases such as 'atom, particle, or molecule' more often than I'd like. For example, Wikipedia defines atomic mass as

the mass of an atomic particle, sub-atomic particle, or molecule.

I remember concise definitions more easily, so a single word for 'molecules and molecular constituents' would be useful.

Is there such a term?

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    $\begingroup$ As a general rule for these definitions, have a the Coloured Books of the IUPAC (International Union of Pure and Applied Chemistry)! In this case, you can find the definitions for molecule and molecular entity in the IUPAC Compendium of Chemical Terminology, known as the Gold Book. $\endgroup$ Commented May 22, 2015 at 15:21
  • $\begingroup$ @KlausWarzecha That's a good answer. Care to put it as an answer? I'd accept it. $\endgroup$
    – Hal
    Commented May 22, 2015 at 15:30

1 Answer 1


This is pretty much link-only, but anyway...

When searching for official definitions, nomenclature, or recommended procedures, the organisation providing all these is the IUPAC (International Union of Pure and Applied Chemistry)!

An IUPAC book series, known as the Colour Books, provides the normative definitions and guidelines on various topics. These are the results of what chemists in the different committees in the IUPAC divisions have eventually agreed upon.

To my knowledge, all these Colour Books are available online.

As kindly mentioned by Loong in a comment, the online versions are not necessary the latest ones! The online version of the IUPAC Nomenclature of Organic Chemistry is from 1993. In addition, a 2004 draft copy is legally available.

Organic chemists will often refer to the Blue Book (Nomenclature of Organic Chemistry), inorganic chemists to the Red Book (Nomenclature of Inorganic Chemistry), etc.

As far as your question is concerned, the Gold Book (IUPAC Compendium of Chemical Terminology) provides the definitions for molecule and molecular entity.

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    $\begingroup$ This is far more than a 'link only' answer - great explanations of the IUPAC online resources $\endgroup$
    – user15489
    Commented May 22, 2015 at 16:01
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    $\begingroup$ Unfortunately, the current version of the Blue Book (2013) is not legally available online yet. You can only find the old recommendations (1979 and 1993). $\endgroup$
    – user7951
    Commented May 22, 2015 at 17:26
  • $\begingroup$ @Loong Yeah they still want you to buy the hardcover book or the online access. Not a very nice thing, since it is very expensive and most organic chemists/ research centers should have access to it. $\endgroup$ Commented May 22, 2015 at 17:50

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