(i) Aluminum oxide or Alumina ( AI₂O₃)

It occurs in nature as colorless corundum and several colored minerals like ruby (red), topaz (yellow), Sapphire (blue), amethyst (violet) and emerald (green). These minerals are used as precious stones (gems).

(ii) Aluminum chloride ( AI₂CI₆ ) : It is prepared by passing dry chlorine over aluminum powder.

AI₂O₃ + 3C + 3CI₂ —→ 2AICI₃ + 3CO(g)
                                      (anhydrous)

It exists as dimer AI₂CI₆ in inert organic solvents and in vapor state. It sublimes at 100^oc under vacuum. Dimeric structure disappears when AICI₃ is dissolved in water. It is hygroscopic in nature and absorbs moisture when exposed to air.

(iii) Thermite : A mixture of aluminum powder and Fe₂O₃ in the ratio 1:3. It is used for welding of iron. The reaction between AI and Fe₂O₃ is highly exothermic,

AI + Fe₂O₃→ AI₂O₃ + Fe Heat

(iv) Aluminium sulphate [Al₂(SO₄)₃] : It is used for the preparation of alums e.g., potash alum AI₂ ( SO₄ )₃ . K₂SO₄ . 24H₂O . It is also used for making fire proof clothes.