Page 87 - Nomenclature of Inorganic Chemistry (IUPAC Recommendations 2005)

C O M P O S I T I O N A L N O M E N C L A T U R E I R-5.4

Several conventions are observed for inferring oxidation numbers, t he use of which is
particularly common in the names of compounds of transition elements. H ydrogen is consi-
dered positive (oxidation number I) in combination with non-metallic elements and negative
(oxidation number I) in combination with metallic elements. Organic g roups combined w ith
metal atoms are treated sometimes as anions (for example, a m ethyl ligand is usually
considered to be a m ethanide ion, CH 3 ), sometimes as neutral (e.g. carbon monooxide).

Bonds between a toms of the same species make n o c ontribution to oxidation number.

Examples:

10. N 2 O n itrogen(I) oxide
nitrogen(IV) oxide
11. NO 2
iron(II) diiron(III) oxide
12. Fe 3 O 4
manganese(IV) oxide
13. MnO 2
14. CO carbon(II) oxide
iron(II) sulfate
15. FeSO 4
iron(III) sulfate
16. Fe 2 (SO 4 ) 3
sulfur(VI) fluoride
17. SF 6
dioxidouranium(V) sulfate
18. (UO 2 ) 2 SO 4
19. UO 2 SO 4 dioxidouranium(VI) sulfate
20. K 4 [Fe(CN) 6 ] p otassium hexacyanidoferrate(II), or potassium
hexacyanidoferrate(4 )
21. K 4 [Ni(CN) 4 ] p otassium tetracyanidonickelate(0), o r p otassium
tetracyanidonickelate(4 )
22. Na 2 [Fe(CO) 4 ] s odium tetracarbonylferrate( II), or sodium
tetracarbonylferrate(2 )
23. [Co(NH 3 ) 6 ]Cl(SO 4 ) h exaamminecobalt(III) chloride sulfate,
or hexaamminecobalt(3þ) c hloride s ulfate

iron(III) hexacyanidoferrate(II), or iron(3þ)
24. Fe 4 [Fe(CN) 6 ] 3
hexacyanidoferrate(4 )
Note that oxidation numbers are no longer recommended when n aming homopolyatomic
ions. This is to avoid a mbiguity. O xidation numbers refer to the individual atoms of the
element in question, e ven if they are appended to a n ame c ontaining a m ultiplicative prefix,
cf. E xample 12 above. To conform to this practice, dimercury(2þ) ( see Section IR-5.3.2.3)
would have to be named dimercury(I); d ioxide(2 ) ( see Section IR-5.3.3.3) would be
dioxide( I); and ions such as pentabismuth(4þ) ( see Section IR-5.3.2.3) and dioxide(1 )
(see Section IR-5.3.3.3), with fractional f ormal oxidation numbers, could n ot be named at all.

IR-5.4.2.3 Multiple m onoatomic c onstituents vs. homopolyatomic constituents

Care should be taken t o d istinguish between m ultiple m onoatomic c onstituents and
polyatomic constituents. This distinction is often not apparent from the formula, but is
tacitly implied.

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