|
|
Atomic Number: |
13 |
Melting Point: | 660.32 ºC | |
| Atomic Symbol: | Al | Boiling Point: | 2519 ºC | ||
| Atomic Weight: | 26.98154 amu | Density: | 2700
kg/m 3 |
||
| Atomic Radius: |
143.1 pm |
Oxidation States: | 3 | ||
| Covalent Radius: | 118 pm | Electron Configuration: | [Ne]3s23p1 | ||
| van der Waals Radius: |
-- |
State of Matter: | solid |
(L. alumen: alum) The ancient Greeks and Romans used alum as an astringent and as a mordant in dyeing. In 1761 de Morveau proposed the name alumine for the base in alum, and Lavoisier, in 1787, thought this to be the oxide of a still undiscovered metal.
Wohler is generally credited with having isolated the metal in 1827, although an impure form was prepared by Oersted two years earlier. In 1807, Davy proposed the name aluminum for the metal, undiscovered at that time, and later agreed to change it to aluminum. Shortly thereafter, the name aluminum was adopted to conform with the "ium" ending of most elements, and this spelling is now in use elsewhere in the world.
Aluminium was also the accepted spelling in the U.S. until 1925, at which time the American Chemical Society officially decided to use the name aluminum thereafter in their publications.
Aluminum is a soft and lightweight but strong metal with a dull silver-gray appearance, due to a thin layer of oxidation that forms quickly when it is exposed to air and which prevents further corrosion. Aluminum weighs about one-third as much as steel or copper; is malleable, ductile, and easily machined and cast; and has excellent corrosion resistance and durability. It is also nonmagnetic and nonsparking and is the second most malleable metal behind gold and the sixth most ductile.
The method of obtaining aluminum metal by the electrolysis of alumina dissolved in cryolite was discovered in 1886 by Hall in the U.S. and at about the same time by Heroult in France. Cryolite, a natural ore found in Greenland, is no longer widely used in commercial production, but has been replaced by an artificial mixture of sodium, aluminum, and calcium fluorides.
Aluminum can now be produced from clay, but the process is not economically feasible at present. Aluminum is the most abundant metal to be found in the earth's crust (8.1%), but is never found free in nature. In addition to the minerals mentioned above, it is also found in granite and in many other common minerals.
It is extensively used for kitchen utensils, outside building decoration, and in thousands of industrial applications where a strong, light, easily constructed material is needed.
Although its electrical conductivity is only about 60% that of copper, it is used in electrical transmission lines because of its light weight. Pure aluminum is soft and lacks strength, but alloyed with small amounts of copper, magnesium, silicon, manganese, or other elements impart a variety of useful properties.
These alloys are of vital importance in the construction of modern aircraft and rockets. Aluminum, evaporated in a vacuum, forms a highly reflective coating for both visible light and radiant heat. These coatings soon form a thin layer of the protective oxide and do not deteriorate as do silver coatings. They are used to coat telescope mirrors and to make decorative paper, packages, and toys.
The compounds of greatest importance are aluminum oxide, the sulfate, and the soluble sulfate with potassium (alum). The oxide, alumina, occurs naturally as ruby (Al2O3), sapphire, corundum, and emery, and is used in glassmaking and refractories. Synthetic ruby and sapphire are used in lasers for producing coherent light.
Aluminium has nine isotopes. Only the stable isotope, Al-27 and the radioactive isotope, Al-26 occur naturally. Al-26 is produced from argon in the atmosphere by spallation caused by cosmic-ray protons. Aluminum isotopes have found practical application in dating marine sediments, manganese nodules, glacial ice, quartz in rock exposures, and meteorites. The ratio of Al-26 to beryllium-10 has been used to study the role of transport, deposition, sediment storage, burial times, and erosion on 105 to 106 year time scales.
Cosmogenic Al-26 was first applied in studies of the Moon and meteorites. Meteorite fragments, after departure from their parent bodies, are exposed to intense cosmic-ray bombardment during their travel through space, causing substantial Al-26 production. After falling to Earth, atmospheric shielding protects the meteorite fragments from further Al-26 production, and its decay can then be used to determine the meteorite's terrestrial age. Meteorite research has also shown that Al-26 was relatively abundant at the time of formation of our planetary system. Possibly, the energy released by the decay of Al-26 was responsible for the remelting and differentiation of some asteroids after their formation 4.6 billion years ago.
Aluminum is one of the few abundant elements that appear to have no beneficial function in living cells, but a few percent of people are allergic to it -- they experience contact dermatitis from any form of it: an itchy rash from using styptic or antiperspirant products, digestive disorders and inability to absorb nutrients from eating food cooked in aluminum pans, and vomiting and other symptoms of poisoning from ingesting such products as Kaopectate®, Amphojel®, and Maalox®. In other persons, aluminum is not considered as toxic as heavy metals, but there is evidence of some toxicity if it is consumed in excessive amounts, although the use of aluminum cookware, popular because of its corrosion resistance and good heat conduction, has not been shown to lead to aluminum toxicity in general. Excessive consumption of antacids containing aluminum compounds and excessive use of aluminum-containing antiperspirants are more likely causes of toxicity. It has been suggested that aluminum may be linked to Alzheimer's disease, although that research has recently been refuted.
