Aluminium is a prominent “group 13” element, a member of the Boron family. Electronic configuration of Aluminium is 1s2 2s2 2p6 3s2 3p1. Due to an additional electron orbit in comparison to Boron, the sum of the first three ionization enthalpies of Aluminium is low in comparison to Boron and is therefore able to form Al3+ ions. It is a highly electropositive element and generally furnishes +3 oxidation states, as in case of Aluminium Oxide (Al2O3). Other known oxidation states are +2 and +1. It is often protected by a layer of inert transparent Aluminium oxide (Al2O3) that forms rapidly in air, but is found to be highly reactive in nature. Aluminium forms amphoteric oxides, that is, it shows both acidic and basic character. Some reactions of Aluminium are:
Reaction of Aluminium with air: Generally, Aluminium metal does not react with air as its surface is covered with a thin layer of oxide that helps protect the metal from attack by air. However, in case the oxide layer gets damaged and the Aluminium metal gets exposed, it reacts again with oxygen forming amphoteric oxide (Aluminium (lll) Oxide), Al2O3.
4Al (s) + 3O2 (l) → 2Al2O3 (s)
Reaction of Aluminium with acids: Aluminium reacts readily with mineral acids to form solutions containing aquated Al (lll) ion along with the liberation of hydrogen gas, H2. For example, it dissolves in hydrochloric acid (HCl) liberating dihydrogen gas.
2Al(s) + 6HCl (aq) → 2Al3+ (aq) + 6Cl– (aq) + 3H2 (g)
In case of reaction with Nitric acid, it reacts passively by forming a protective oxide layer on its surface of Aluminium Oxide.
Al2O3 +6 HNO3 → 2Al(NO3)3 + 3H2O
Reaction of Aluminium with alkalis: Aluminium reacts with alkalis to form aluminates along with the liberation of hydrogen gas, H2. Comparable electronegativity of Oxygen and Aluminium makes it possible for Aluminium to form covalent bonds with oxygen. This can be seen as a prominent reason for the formation of aluminates. For example, Aluminum reacts with hot, concentrated sodium hydroxide solution to produce a colorless solution of sodium tetrahydroxoaluminate along with the evolution of dihydrogen gas.
2Al (s) + 2NaOH (aq) + 6H2O → 2Na+ (aq) + 2[Al(OH)4]– + 3H2 (g)
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