The chemical element aluminum is classed as an other metal. It was discovered in the 1750s by Andreas Marggraf.
|Classification:||Aluminum is an ‘other metal’|
|Atomic weight:||26.98154 g/mol|
|Melting point:||660.32 oC, 933.57 K|
|Boiling point:||2466.85 oC, 2740.00 K|
|Neutrons in most abundant isotope:||14|
|Electron configuration:||1s2 2s2 2p6 3s2 3p1|
|Density @ 20oC:||2.702 g/cm3|
Reactions, Compounds, Radii, Conductivities
|Atomic volume:||9.98 cm3/mol|
|Structure:||fcc: face-centered cubic|
|Specific heat capacity||0.90 J g-1 K-1|
|Heat of fusion||10.790 kJ mol-1|
|Heat of atomization||326 kJ mol-1|
|Heat of vaporization||293.40 kJ mol-1|
|1st ionization energy||577.6 kJ mol-1|
|2nd ionization energy||1816.6 kJ mol-1|
|3rd ionization energy||2744.7 kJ mol-1|
|Electron affinity||42.6 kJ mol-1|
|Minimum oxidation number||0|
|Min. common oxidation no.||0|
|Maximum oxidation number||3|
|Max. common oxidation no.||3|
|Electronegativity (Pauling Scale)||1.61|
|Polarizability volume||8.3 Å3|
|Reaction with air||mild, w/ht ⇒ Al2O3|
|Reaction with 15 M HNO3||passivated|
|Reaction with 6 M HCl||mild, ⇒ H2, AlCl3|
|Reaction with 6 M NaOH||mild, ⇒ H2, [Al(OH)4]–|
|Chloride(s)||AlCl3 & Al2Cl6|
|Atomic radius||125 pm|
|Ionic radius (1+ ion)||–|
|Ionic radius (2+ ion)||–|
|Ionic radius (3+ ion)||53.5 pm|
|Ionic radius (1- ion)||–|
|Ionic radius (2- ion)||–|
|Ionic radius (3- ion)||–|
|Thermal conductivity||237 W m-1 K-1|
|Electrical conductivity||37.6676 x 106 S m-1|
|Freezing/Melting point:||660.32 oC, 933.57 K|
Discovery of Aluminum
People have used alum since ancient times for dyeing, tanning and to stop bleeding. Alum is potassium aluminum sulfate.
In the 1750s German chemist Andreas Marggraf found he could use an alkali solution to precipitate a new substance from alum. Marggraf had previously been the first person to isolate zinc in 1746.
The substance Marggraf obtained from alum was named alumina by French chemist Louis de Morveau in 1760. We now know that alumina is aluminum oxide – chemical formula Al2O3.
De Morveau believed alumina contained a new metallic element, but, like Marggraf, he was unable to extract this metal from its oxide. (1), (2)
In 1807 or 1808, English chemist Humphry Davy decomposed alumina in an electric arc to obtain a metal. The metal was not pure aluminum, but an alloy of aluminum and iron.
Davy called the new metal alumium, then renamed it aluminum. (3)
Aluminum was first isolated in 1825 by Hans Christian Ørsted (Oersted) in Copenhagen, Denmark who reported, “a lump of metal which in color and luster somewhat resembles tin.”
Ørsted produced aluminum by reducing aluminum chloride using a potassium-mercury amalgam. The mercury was removed by heating to leave aluminum.
German chemist Friedrich Wöhler (Woehler) repeated Ørsted’s experiment but found it yielded only potassium metal. Wöhler developed the method further two years later, reacting volatalized aluminum trichloride with potassium to produce small amounts of aluminum. (1)
In 1856 Berzelius stated that it was Wöhler who had succeeded in 1827. Wöhler is therefore usually given credit for the discovery.
More recently, Fogh repeated the original experiments and has shown that Ørsted’s method can give satisfactory results.
This has strengthened the priority of Ørsted’s original work and his position as discoverer of aluminum. (4)
For almost three decades, aluminum remained a novelty, expensive to produce and more valuable than gold, until in 1854 Henri Saint-Claire Deville in Paris, France found a way of replacing potassium with much cheaper sodium in the reaction to isolate aluminum. Aluminum then became more popular but, because it was still quite expensive, was used in ornamental rather than practical situations.
Finally, in 1886 American chemist Charles Martin Hall and French chemist Paul Héroult independently invented the Hall-Héroult process, which inexpensively isolates aluminum metal from its oxide electrolytically.
Aluminum is still manufactured using the Hall-Héroult process today.
Interesting Facts about Aluminum
- 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. (5)
- Aluminum is a great metal to recycle. Recycling uses only 5% of the energy needed to produce aluminum from its ore, bauxite. (6)
- 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.) (7)
Appearance and Characteristics
No proven issues; ingestion may cause alzheimer’s disease
Aluminum is a silvery-white metal. It does not stick to magnets (it is paramagnetic and so its magnetism under normal conditions is very, very weak). It is an excellent electrical conductor. It is of low density and high ductility. It is too reactive to be commonly found as the metal although, very rarely, the native metal can be found. (8)
Aluminum’s appearance is dulled and its reactivity is passivated by a film of aluminum oxide that naturally forms on the surface of the metal under normal conditions. The oxide film results in a material that resists corrosion. The film can be thickened using electrolysis or oxidizing agents and aluminum in this form will resist attack by dilute acids, dilute alkalis and concentrated nitric acid.
Aluminum lies sufficiently far on the right side of the periodic table that it shows some hints of nonmetal behavior, reacting with hot alkalis to form aluminate ions [Al(OH)4]– as well as the more typical metal reaction with acids to release hydrogen gas and form the positively charged metal ion, Al3+. i.e. aluminum is amphoteric.
Pure aluminum is quite soft and lacking in strength. Aluminum used in commercial applications has small amounts of silicon and iron (less than 1%) added, resulting in greatly improved strength and hardness.
Uses of Aluminum
As a result of its low density, low cost, and corrosion resistance, aluminum is widely used around the world.
It is used in an extensive range of products from drinks cans to window frames and boats to aircraft. A Boeing 747-400 contains 147,000 pounds (66,150 kg) of high-strength aluminum.
Unlike some metals, aluminum has no aroma – hence its widespread use in food packaging and cooking pots.
Although not quite as good as silver or copper, aluminum is an excellent electrical conductor. It is also considerably cheaper and lighter than these metals, so it is used widely in overhead power lines.
Of all the metals, only iron is used more widely than aluminum.
Abundance and Isotopes
Abundance earth’s crust: 8.23 % by weight, 6.32 % by moles
Abundance solar system: 56 ppm by weight, 2.7 ppm by moles
Cost, pure: $15.72 per 100g
Cost, bulk: $0.20 per 100g
Source: Aluminum is the most abundant metal in the earth’s crust and the third most element in the earth’s crust, after oxygen and silicon. Aluminum is too reactive to be found pure. Bauxite (mainly aluminum oxide) is the most important ore.
Isotopes: 15 whose half-lives are known, mass numbers 22 to 35. Of these, only two occur naturally: 27Al, which is stable, and 26Al, which is radioactive with half-life is 7.17 x 105 years. 26Al is formed by cosmic-ray bombardment of argon in Earth’s atmosphere.
- Ian McNeil, Encyclopaedia of the History of Technology., (1996) p102. Routledge
- David R. Lide, CRC Handbook of Chemistry and Physics., (2007) 4-3. CRC
- Halvor Kvande, Two hundred years of aluminum … or is it aluminium?, Journal of the Minerals, Metals and Materials Society, (2008) Volume 60, Number 8: p23-24.
- China’s aluminum foil, Wall Street Journal
- Paolo Ventura, Roberta Carini, Francesca D’Antona, A deep insight into the Mg-Al nucleosynthesis in massive AGBs and SAGB stars., Mon. Not. R. Astron. Soc., 2002.
- Burrows et al., Chemistry3, (2009) Oxford University Press, p1201.
- Dekov et al., American Mineralogist., (2009) 94: p1283-1286.
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