AluminiumIII

Aluminium(III) refers to aluminium in the +3 oxidation state, commonly written as aluminium(III) or Al3+. It is the most stable and widespread oxidation state for aluminium in its compounds. In aqueous solution, Al3+ exists primarily as the hexaaqua complex [Al(H2O)6]3+, which slowly hydrolyzes to form various hydroxo species and aluminium hydroxide as the pH increases.

Aluminium(III) is a hard Lewis acid with high charge density, preferring oxygen donors. It forms a range of coordination compounds with oxide, hydroxide and fluoride ligands, as well as with organic ligands. The chemistry of Al3+ is dominated by hydrolysis, precipitation, and formation of polycations such as [Al(OH)4]− in basic solutions.

Common aluminium(III) compounds include aluminum oxide (alumina, Al2O3), aluminium hydroxide Al(OH)3, and aluminium chloride AlCl3. Al2O3 is a major mineral and industrial material; alumina is used as a refractory ceramic, abrasive, catalyst support, and in electronic substrates. Al(OH)3 is used in antacids and as a flocculant in water treatment. AlCl3 is a versatile Lewis acid catalyst. In basic solution, aluminium forms aluminates such as [Al(OH)4]−.

Occurrence and production: aluminium is the most abundant metal in the Earth's crust and the third most abundant element overall, primarily found as oxides in bauxite. It is refined to pure aluminium metal via the Hall–Héroult process, beginning with the extraction of alumina from bauxite.

Safety and biology: aluminium(III) ions are not known to be essential for living organisms. Exposure to high levels can be toxic, and industrial use typically follows regulatory guidelines to minimize risk.