Page 51 - Nomenclature of Inorganic Chemistry (IUPAC Recommendations 2005)

G R A M M A R I R-2.15

IR-2.15.3 Other ordering rules

IR-2.15.3.1 Element ordering on the basis of the periodic table
One important element sequence based on the periodic table is shown i n T able VI. The
element columns (1 to 18) are connected b y a rrows leading in a d irection starting from
the less metallic elements and moving towards t he more m etallic elements. Only H h as a
unique p osition. This order has its origin in electronegativity considerations even though O
is now placed at its usual position in group 16. It is used for ordering e lement symbols and
element names in the following cases.
(a) In compositional names of binary compounds and corresponding formulae, the element
encountered last when f ollowing t he arrow in Table VI is represented first in the formula
as well as the name.

Examples:

1. S 2 Cl 2 disulfur dichloride
2. O 2 Cl dioxygen chloride
3. H 2 Te dihydrogen telluride
4. AlH 3 aluminium trihydride

(b) In additive names of polynuclear compounds, the central atom encountered last when
following the arrow is listed first, cf. S ections IR-7.3.2 and IR-9.2.5.1.

(c) In additive names for chains and rings, to determine the numbering of the skeletal atoms
if this is not defined fully by the structure of the skeleton. The element encountered first
when following the arrows in Table VI is given the lowest number. Note that the element
‘y’ terms (Table X) are cited alphabetically.

Example:
5. HOS(O) 2 SeSH
1,4-dihydrido-2,2-dioxido-1-oxy-3-seleny-2,4-disulfy-[4]catena
(d) In Hantzsch–Widman n ames, the element encountered first when f ollowing the arrows in
Table VI is given the lowest number. The element ‘a’ terms (Table X) are cited in the same
order.

Examples:

6: 1 7: 1
4 O 2 4 O 2
HSb SbH HSb SbH
S Se
3 3
1,3,2,4-oxathiadistibetane 1,3,2,4-oxaselenadistibetane

(e) In names where heteroatoms replacing s keleton atoms are indicated by ‘a’ prefixes, the
element encountered first when following the arrows in Table VI is given the lowest number.
The element ‘a’ terms (Table X ) a re cited in the same o rder.

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