Aluminium metal reacting in a test tube with the liquid halogen element bromine. The reaction is vigorous, producing sparks, flames and thick clouds of aluminium bromide smoke. The equation for the reaction is: 2Al + 3Br2 --> 2AlBr3. Aluminium bromide exists as a dimer, made up of two AlBr3 molecules, so the species is more accurately described as Al2Br6.