of a skeletal atom is the sum of the total number of bonding equivalents (valence bonds) of that skeletal atom to adjacent skeletal atoms in a parent hydride, if any, and the number of attached hydrogen atoms, if any. Examples:
SH2:
for S,
;
SH6:
for S,
.
Source:
See also:
PAC, 1984, 56, 769
(Treatment of variable valence in organic nomenclature (lambda convention) (Recommendations 1983))
on page 774