Aluminium is a soft, silvery light metal. It is very reactive so that in the atmosphere a thin but equally protective oxide layer forms rapidly. For this reason it is very resistant to corrosion. By a special treatment, anodizing, i. e. an electrolytic oxidation process, the aluminum surface protected by the oxide layer can even be strengthened and made more resistant to corrosion.
Aluminium reacts strongly with hydrochloric acid and caustic soda. The reaction with sulfuric acid is weaker, while it remains passive in contact with cold nitric acid.
Aluminium possesses good thermal and electrical conductivity, in each case about two-thirds of the values for pure copper. Due to its electronic configuration the element has three valency electrons; its oxidation number is therefore +3.