Aluminum (or Aluminium elsewhere in the world) (13)

Pure aluminium is a silvery-white metal with many desirable characteristics. It is light, nontoxic (as the metal), nonmagnetic and nonsparking. It is somewhat decorative. It is easily formed, machined, and cast. Pure aluminium is soft and lacks strength, but alloys with small amounts of copper, magnesium, silicon, manganese, and other elements have very useful properties. Aluminium is an abundant element in the earth's crust, but it is not found free in nature. The Bayer process is used to refine aluminium from bauxite, an aluminium ore.

•Name: Aluminium
•Symbol: Al
•Atomic number: 13
•Atomic weight: 26.9815386
•Standard state: solid at 298 K
•CAS Registry ID: 7429-90-5
•Group in periodic table: 13
•Period in periodic table: 3
•Block in periodic table: p-block
•Color: silvery
•Classification: Metallic

Historical information

Aluminium was discovered by Hans Christian Oersted at 1825 in Denmark. Origin of name: from the Latin word "alumen" meaning "alum".The ancient Greeks and Romans used alum in medicine as an astringent [meaning contracting, constrictive, styptic, harshly biting, or caustic], and in dyeing processes. In 1761 de Morveau proposed the name "alumine" for the base in alum. In 1807, Davy proposed the name alumium for the metal, undiscovered at that time, and later agreed to change it to aluminum. Shortly thereafter, the name aluminium was adopted by IUPAC to conform to the "ium" ending of most elements. Aluminium is the IUPAC spellingand therefore the international standard. Aluminium was also the accepted spelling in the U.S.A. until 1925, at which time the American Chemical Society decided to revert back to aluminum, and to this day Americans still refer to aluminium as "aluminum".

Aluminium is one of the elements which as alum or alumen, KAl(SO4)2, has an alchemical symbol (a simple circle). Alchemy is an ancient pursuit concerned with, for instance, the transformation of other metals into gold.

Aluminium was first isolated by Hans Christian Oersted in 1825 who reacted aluminium chloride (AlCl3) with potassium amalgam (an alloy of potassium and mercury). Heating the resulting aluminium amalgam under reduced pressure caused the mercury to boil away leaving an impure sample of aluminium metal.

Physical properties

•Melting point: 933.47 [or 660.32 °C (1220.58 °F)] K
•Boiling point: 2792 [or 2519 °C (4566 °F)] K
•Density of solid: 2700 kg m-3

Orbital properties

•Ground state electron configuration: [Ne].3s2.3p1
•Shell structure: 2.8.3
•Term symbol: 2P1/2

Isolation

Aluminium would not normally be made in the laboratory as it is so readily available commercially.

Aluminium is mined in huge scales as bauxite (typically Al2O3.2H2O). Bauxite contains Fe2O3, SiO2, and other impurities. In order to isolate pure aluminium, these impurities must be removed from the bauxite. This is done by the Bayer process. This involves treatment with sodium hydroxide (NaOH) solution, which results in a solution of sodium aluminate and sodium silicate. The iron remains behind as a solid. When CO2 is blown through the resulting solution, the sodium silicate stays in solution while the aluminium is precipitated out as aluminium hydroxide. The hydroxide can be filtered off, washed, and heated to form pure alumina, Al2O3.

The next stage is formation of pure aluminium. This is obtained from the pure Al2O3 by an electrolytic method. Electrolysis is necessary as aluminium is so electropositive. It seems these days that electrolysis of the hot oxide in a carbon lined steel cell acting as the cathode with carbon anodes is most common.

Interesting facts (let me know if you like these!)

•Aluminum manufacturing takes a lot of energy – 17.4 megawatt hours of electrical energy to produce one metric ton of aluminum; that’s three times more energy than is needed to make a metric ton of steel.

•Aluminum is a great metal to recycle. Recycling uses only 5% of the energy needed to produce aluminum from its ore, bauxite.

•Aluminum does not stick to magnets under normal conditions.

•There is more aluminum in the Earth’s crust than any other metal. At about 8 percent, aluminum is the third most abundant element in our planet’s crust, behind oxygen and silicon.

•Despite its high abundance, in the 1850s aluminum was more valuable than gold. In 1852 aluminum was priced at $1200 per kg and gold was $664 per kg.

•Aluminum prices illustrate the perils of financial speculation: in 1854 Saint-Claire Deville found a way of replacing potassium with much cheaper sodium in the reaction to isolate aluminum. By 1859, aluminum was priced at $37 per kg; its price had dropped 97% in just five years.

•Where the previous item highlights the perils of speculation, this item highlights one of the triumphs of chemistry: the Hall-Heroult electrolytic process was discovered in 1886. By 1895, aluminum’s price had dropped to just $1.20 per kg.

•Ruby gemstones are mainly aluminum oxide in which a small number of the aluminum ions have been replaced by chromium ions.

•Aluminum is made in the nuclear fires of heavy stars when a proton adds to magnesium. (Magnesium is itself made in stars by nuclear fusion of two carbons.)