[(HO) 3 AlOAl(OH) 3 ]2–, are also present.
See also aluminium hydroxide.
aluminiumSymbol Al. A silvery-
white lustrous metallic element be-
longing to *group 3 (formerly IIIB) of
the periodic table; a.n. 13; r.a.m.
26.98; r.d. 2.7; m.p. 660°C; b.p.
2467 °C. The metal itself is highly re-
active but is protected by a thin
transparent layer of the oxide, which
forms quickly in air. Aluminium and
its oxide are amphoteric. The metal
is extracted from puriÜed bauxite
(Al 2 O 3 ) by electrolysis; the main
process uses a *Hall–Heroult cell but
other electrolytic methods are under
development, including conversion
of bauxite with chlorine and electrol-
ysis of the molten chloride. Pure alu-
minium is soft and ductile but its
strength can be increased by work-
hardening. A large number of alloys
are manufactured; alloying elements
include copper, manganese, silicon,
zinc, and magnesium. Its lightness,
strength (when alloyed), corrosion re-
sistance, and electrical conductivity
(62% of that of copper) make it suit-
able for a variety of uses, including
vehicle and aircraft construction,
building (window and door frames),
and overhead power cables. Al-
though it is the third most abundant
element in the earth’s crust (8.1% by
weight) it was not isolated until 1825
by H. C. *Oersted.
A- Information from the WebElements site
aluminium acetateSee alu-
minium ethanoate.aluminium chlorideA whitish
solid, AlCl 3 , which fumes in moist air
and reacts violently with water (to
give hydrogen chloride). It is known
as the anhydrous salt (hexagonal; r.d.
2.44 (fused solid); m.p. 190°C (2.5
atm.); sublimes at 178°C) or the hexa-
hydrate AlCl 3 .6H 2 O (rhombic; r.d.aluminium 24a
ClCl ClClAl Al
ClClAluminium chloride2.398; loses water at 100°C), both of
which are deliquescent. Aluminium
chloride may be prepared by passing
hydrogen chloride or chlorine over
hot aluminium or (industrially) by
passing chlorine over heated alu-
minium oxide and carbon. The chlo-
ride ion is polarized by the small
positive aluminium ion and the
bonding in the solid is intermediate
between covalent and ionic. In the
liquid and vapour phases dimer mol-
ecules exist, Al 2 Cl 6 , in which there
are chlorine bridges making coordi-
nate bonds to aluminium atoms (see
formula). The AlCl 3 molecule can also
form compounds with other mol-
ecules that donate pairs of electrons
(e.g. amines or hydrogen sulphide);
i.e. it acts as a Lewis *acid. At high
temperatures the Al 2 Cl 6 molecules in
the vapour dissociate to (planar)
AlCl 3 molecules. Aluminium chloride
is used commercially as a catalyst in
the cracking of oils. It is also a cata-
lyst in certain other organic reac-
tions, especially the Friedel–Crafts
reaction.aluminium ethanoate (aluminium
acetate)A white solid, Al(OOCCH 3 ) 3 ,
which decomposes on heating, is
very slightly soluble in cold water,
and decomposes in warm water. The
normal salt, Al(OOCCH 3 ) 3 , can only
be made in the absence of water (e.g.
ethanoic anhydride and aluminium
chloride at 180°C); in water it forms
the basic salts Al(OH)(OOCCH 3 ) 2 and
Al 2 (OH) 2 (OOCCH 3 ) 4. The reaction of
aluminium hydroxide with ethanoic
acid gives these basic salts directly.
The compound is used extensively in
dyeing as a mordant, particularly in