5- membered rings have olefor un-
saturated and olanefor saturated
compounds. Rules are given for nam-
ing compounds with two or more
different heteroatoms and for num-
bering the atoms. The system is
widely used both for monocyclic
compounds and for heterocyclic com-
ponents of polycyclic compounds.
A- Information about IUPAC nomenclature
hapticitySymbol η. The number of
electrons in a ligand that are directly
coordinated to a metal.
hard acid See hsab principle.
hard base See hsab principle.
hardening of oils The process of
converting unsaturated esters of
*fatty acids into (more solid) satu-
rated esters by hydrogenation using a
nickel catalyst. It is used in the man-
ufacture of margarine from vegetable
oils.hardness of water The presence
in water of dissolved calcium or mag-
nesium ions, which form a scum
with soap and prevent the formation
of a lather. The main cause of hard
water is dissolved calcium hydrogen-
carbonate (Ca(HCO 3 ) 2 ), which is
formed in limestone or chalk regions
by the action of dissolved carbon
dioxide on calcium carbonate. This
type is known as temporary hardness
because it is removed by boiling:
Ca(HCO 3 ) 2 (aq) →CaCO 3 (s) + H 2 O(l)
+ CO 2 (g)
The precipitated calcium carbonate is
the ‘fur’ (or ‘scale’) formed in kettles,
boilers, pipes, etc. In some areas,
hardness also results from dissolved
calcium sulphate (CaSO 4 ), which can-
not be removed by boiling (perma-
nent hardness).
Hard water is a considerable prob-
lem in washing, reducing the efÜ-
ciency of boilers, heating systems,etc., and in certain industrial
processes. Various methods of water
softeningare used. In public sup-
plies, the temporary hardness can be
removed by adding lime (calcium hy-
droxide), which precipitates calcium
carbonate
Ca(OH) 2 (aq) + Ca(HCO 3 ) 2 (aq) →
2CaCO 3 (s) + 2H 2 O(l)
This is known as the Clark process (or
as ‘clarking’). It does not remove per-
manent hardness. Both temporary
and permanent hardness can be
treated by precipitating calcium car-
bonate by added sodium carbonate –
hence its use as a washing soda and
in bath salts. Calcium (and other)
ions can also be removed from water
by ion-exchange using zeolites (e.g.
Permutit). This method is used in
small domestic water-softeners. An-
other technique is not to remove the
Ca2+ions but to complex them and
prevent them reacting further. For
domestic use polyphosphates (con-
taining the ion P 6 O 18 6–, e.g. Calgon)
are added. Other sequestering agents
are also used for industrial water. See
also sequestration.Hargreaves process See potas-
sium sulphate.harmonicAn oscillation having a
frequency that is a simple multiple
of a fundamentalsinusoidal oscilla-
tion. The fundamental frequency of a
sinusoidal oscillation is usually called
the Ürst harmonic. The second har-
monichas a frequency twice that of
the fundamental, and so on.harmonic oscillatorA system that
oscillates with simple harmonic mo-
tion. The harmonic oscillator is ex-
actly soluble in both classical
mechanics and quantum mechanics.
Many systems exist for which har-
monic oscillators provide very good
approximations. Atoms vibrating
about their mean positions in mol-hapticity 264h