Page 70 - Nomenclature of Inorganic Chemistry (IUPAC Recommendations 2005)

IR-4.4 F O R M U L A E

For inorganic oxoacids, there is a t raditional ordering o f f ormulae in which the ‘acid’ or
‘replaceable’ hydrogen atoms (hydrogen atoms bound to oxygen) are listed fi rst, followed by
the central atom, then ‘non-replaceable’ hydrogen atoms (hydrogen atoms bound directly to
the central atom), and finally oxygen. This format is an alternative to writing the formulae as
coordination compound formulae (see Section IR-8.3).

Examples:
22. HNO 3 (traditional) or [NO 2 (OH)] (coordination)
23. H 2 PHO 3 (traditional) or [PHO(OH) 2 ] ( coordination)

24. H 2 PO 4 (traditional) or [PO 2 (OH) 2 ] (coordination)

25. H 5 P 3 O 10 (traditional) or [(HO) 2 P(O)OP(O)(OH)OP(O)(OH) 2 ] ( coordination)
26. (HBO 2 ) n (traditional) or (-B(OH)O)- n (coordination)

IR-4.4.3.3 Chain compounds

For chain compounds containing three or more d ifferent elements, the sequence of atomic
symbols should generally be in accord with the order in which the atoms are bound in the
molecule or ion, rather than using a lphabetical order or order based on electronegativity.
However, if one wishes to view a c ompound formally as a c oordination c ompound,
e.g. in connection with a d iscussion of additive naming of the compound, one may use
a c oordination-compound t ype of formula, as in Example 1 b elow.

Examples:

1. NCS or SCN (not CNS ) ¼ [C(N)S] , n itridosulfidocarbonate(1 )
2. BrSCN (not BrCNS)
3. HOCN (cyanic acid)
4. HNCO (isocyanic acid)
IR-4.4.3.4 Generalized salt formulae

If the formula of a c ompound containing three or more e lements is not naturally assigned
using the preceding two sections, the compound can be treated as a g eneralized salt. This
term is taken to mean any compound in which it is possible t o i dentify at least one
constituent w hich is a p ositive ion or can be classified as electropositive or more
electropositive than the other c onstituents, and at least one constituent w hich is a n egative
ion or can be classified as electronegative or more electronegative than the rest of the
constitutents. The ordering principle is then:

(i) all electropositive constituents precede all electronegative constituents;
(ii) within each of the two groups of constituents, alphabetical order is used.

Examples:

1. KMgF 3
2. MgCl(OH)

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