History and Production
From Latin alumen, meaning bitter salt. It derives its name from alum, KAl(SO4)2.12H2O, where the ancient Greek and Roman used it in medicine as an astringent and as a mordant in dyeing. In 1807, H. Davy, who was not able to isolate the metal, proposed the name alumium and later changed to aluminum.It was then modified again to the name aluminium. The impure metal was first isolated by H.C. Oersted using the reaction of dilute potassium amalgam on aluminium(III) chloride, in 1825.
Nowadays, it can be obtained by electrolysis of alumina (Al2O3) dissolved in cryolite. The former can be obtained from bauxite mineral via the Bayer process, while cryolite has been largely synthesized since the natural mineral is rather rare. Aluminium is used for kitchen utensils, and a variety industrial and building materials. When alloyed with small amount of other metals such as magnesium, copper, manganese etc, it is
used for construction of aircrafts and rockets. It is also used in coating applications in telescope mirrors, packages, etc.
It is a silvery-white metal, light and nontoxic. It has a high thermal conductivity and excellent corrosion resistance, due to the formation of oxide films on the surface. It is second most malleable (after gold) and very ductile. It is the most abundant metal in the earth's crust, about 8.3% by weight. It is a major constituent of igneous minerals such as micas and feldspars.
Interatomic distance: 286.4 pm
Melting point: 660.3°C
Boiling point: 2519°C
Thermal conductivity/Wm-1K-1: 237 (27°C)
Density/kgm-3: 2698 (20°C), 2390 (m.p.)
Standard Thermodynamic Data (atomic gas)
Enthalpy of formation: 330 kJ/mol
Gibbs free energy of formation: 289.4 kJ/mol
Entropy: 164.6 J/mol K
Heat capacity: 21.4 J/mol K
Electronic configuration: [Ne] 3s2 3p1
Term symbol: 2P1/2
Electron affinity: 41.7618 kJ/mol Electronegativity (Pauline): 1.61
Ionization energy (first, second, third): 577.539, 1816.68, 2744.78 kJ/mol
Aluminium usually exists as Al3+ species in compounds. The formation of trivalent involves large amount of energy and it usually form covalent bonds via sp2 hybridization. The large positive charge, however, can be stabilized by water molecules arranged in
octahedral structures, [Al(H2O)6]3+. This waters of hydration exist both in aqueous and some of the aluminium salts, such as alums.
Test for aluminium:
(1) Addition of ammonia water to a solution of an aluminium salt gives a white gelatinous precipitate of aluminium hydroxide which is insoluble in excess of ammonia. However the precipitate does dissolve in excess sodium hydroxide solution.
(2) Heating the solid aluminium compouind on a charcoal block gives a white residue. It this be moistened with aqueous cobalt nitrate and reheated, a blue aluminate of cobalt is obtained.
(3) Addition of ammonia solution to an aluminium salt in presence of alizarin gives a pink precipitate or 'lake'.