Chemistry of Aluminum
Table of contents
Aluminum, also called Aluminium, is the third most abundant element in the earth's crust. It is commonly used in the household as aluminum foil, in crafts such as dyeing and pottery, and also in construction to make alloys.
History of Aluminum
While aluminum had been used long before the 19th century, it was first isolated in 1825 by Hans Christian Oersted, although not in a very pure form. Before this, it was known for being part of alum, which is used as a mordant to help set dye on fabric. At this time it was known as a very expensive metal. In the late 1800s, two scientists, Charles Martin Hall and Paul L. T. Heroult, found that they could produce aluminum from aluminum oxide through electrolysis and a cryolite (molten mineral) solvent. This allowed the price to decrease and for aluminum to become available for commercial use.
Aluminum on Earth
Aluminum is the third most abundant element found on earth, and the most abundant metal. It makes up 8.1% of the earth's crust by mass, following oxygen and silicon. Naturally, it is found in chemical compounds with other elements like bauxite. It is not easily removed from natural ores because it must first be reduced. To see how alumina, which is used to make aluminum, is extracted from bauxite, read the Bayer Process in the refining aluminum section.
Electron Configuration of Aluminum
To find the electron configuration of an atom, you first need to know the number of electrons that it has. Since aluminum's atomic number is thirteen, it has thirteen electrons. You then split the electrons between the different orbitals. Aluminum's first two electrons fall in the 1s orbital, and the following two electrons go in the 2s orbital. The next six electrons fill the 2p orbital in the second shell (that's ten electrons so far, three more to go). Then electrons 11 and 12 fill the 3s orbital. Finally the last electron occupies the 3p orbital.
The electron configuration for Aluminum is 1s22s22p63s23p1. The ground state electron configuration is [Ne]3s23p1.
Aluminum has three oxidation states. The most common one is +3. The other two are +1 and +2. One +3 oxidation state for Aluminum can be found in the compound aluminum oxide, Al2O3. In AlO, aluminum monoxide, it has a +2 oxidation state, and AlH has an oxidation state of +1.
Aluminum is often combined with oxygen to make ionic compounds. Alumina, Al2O3, is the refractory oxide of aluminum. It is found in bauxite and corundum. It has a very high melting point. One of the applications of this compound is used to produce different color light that can be used as a laser beam. It is also used in pottery, dyeing, antacid medicines, and in making chemicals.
Another compound containing aluminum is Al(OH)3, which is usually formed as a gelatinous precipitate when aluminum compounds are hydrolyzed in water.
Aluminum sulfate, Al2(SO4)3·18H2O is a very useful aluminum compound, made from the oxide and sulfuric acid. One use of this salt is in the dyeing of cotton fabrics.
Aluminum is easily oxidized to Al3+such as in this equation:
2Al(s) + 6H+(aq) → 2Al3+ +3H2(g)
In the welding of large objects, the thermite reaction is used:
2Al(s) + Fe2O3(s) → Al2O3(s) + Fe(s)
Reactions with Halides
Aluminum Halides, like the boron halides, are reactive Lewis Acids, meaning that they readily accept a pair of electrons. For example an important halide complex for the production with aluminum is cryolite, NaAlF6.
6 HF +Al(OH)3 + 3NaOH → Na3AlF6 +6 H2O
Aluminum Oxide and Hydroxide
Aluminum oxide is often referred to as alumina or when is crystalized form, corundum. Aluminum oxide is relatively unreactive because the small Al3+ ions and the O2+ form a very stable ionic lattice in cubic closet structure with the ions occupying small octahedral holes. Aluminum is protected against corrosion due to thin coating of Al2O3 which prevent further oxidation of the aluminum metal.
2Al(s) +3H2O(l) → Al2O3(s) +6H+ +6e-
Aluminum hydroxide is amphoteric which means that it can react with acids or bases.
Acid: Al(OH)3 (s) +3H3O+ (aq) → [Al(H2O)6]3+ (aq)
Base: Al(OH)3 (s) +OH-(aq) → [Al(OH)4]- (aq)
Since aluminum is found in compounds with other elements it needs to be reduced. The Bayer process was invented by Karl Bayer in 1887. It is essentially referring to the refining of bauxite, the most important aluminum ore, to produce alumina. From here, the intermediate alumina must be smelted into metallic aluminum through the Hall-Heroult Process.
1. 1s2 2s2 2p6, or [Ne]
2. It forms a dimer.
3. a) 2Al(s) → Al3+ (aq) + 3e-
b) 2Al(s) + 3Pb+ (aq) → 2Al3+ (aq) + 3Pb(s)
5. Bayer Process
6.1 Al(OH)3 (s) +OH-(aq) → [Al(OH)4]-(aq)
6.2 Al(OH)3(s) + 3H+(aq) → Al(H2O)3]3+(aq)
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