Page 58 - Nomenclature of Inorganic Chemistry (IUPAC Recommendations 2005)

IR-3.4 E L E M E N T S

IR-3.4.2 Allotropes ( allotropic m odifications) of elements
Allotropic modifications of an element bear the name o f t he atom from which they are
derived, together w ith a d escriptor to specify the modification. Common descriptors a re
Greek letters (a, b, g, etc.), colours and, where appropriate, mineral names (e.g. g raphite and
diamond for the well known forms of carbon). Such names should be regarded as
provisional, to be used only until structures h ave been established, after which a r ational
system based on molecular formula (see Section IR-3.4.3) or crystal structure (see Section
IR-3.4.4) is recommended. Common names will continue to be used for amorphous
modifications of an element a nd for those which are mixtures of closely related structures in
their commonly occurring forms (such a s g raphite) or have an ill-defined disordered
structure (such as red phosphorus) (see Section IR-3.4.5).

IR-3.4.3 Names of allotropes of definite molecular formula

Systematic names are based on the number of atoms in the molecule, indicated by a
multiplicative prefix from Table IV. The p refix ‘mono’ is only used when the element does
not normally occur in a m onoatomic state. If the number is large and unknown, as in long
chains or large rings, the prefix ‘poly’ may be used. Where necessary, appropriate prefixes
(Table V) may be used to indicate structure. W hen it is desired to specify a p articular
polymorph of an element with a d efined structure (such a s t he a-, b- o r g-forms of S 8 ) t he
method of Section IR-3.4.4 should be used (see Examples 1 3–15 in Section IR-3.4.4).
Examples:

Formula Systematic name Acceptable a lternative name
1. Ar argon
2. H m onohydrogen
3. N m ononitrogen
4. N 2 dinitrogen
5. N 3 * trinitrogen( * )
6. O 2 dioxygen oxygen
7. O 3 trioxygen ozone
8. P 4 tetraphosphorus white phosphorus
9. S 6 hexasulfur e-sulfur
10. S 8 cyclo-octasulfur a-sulfur, b-sulfur, g-sulfur
11. S n polysulfur m-sulfur (or plastic sulfur)
12. C 60 hexacontacarbon [60]fullerene

In Example 12, the name [ 60]fullerene is to be regarded as an acceptable non-systematic
name for a p articular C 60 structure. For more d etails see Section P-27 of Ref. 6.

IR-3.4.4 Crystalline allotropic modifications of an element
Crystalline allotropic m odifications are polymorphs of the elements. Each can be named by
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adding the Pearson symbol (see Section IR-11.5.2) in parentheses after the name of the

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