We know that Al2O3 is the formula of aluminium oxide. We also know that this formula comes from the criss-cross of the valencies of aluminium and oxygen and the electronic configuration of aluminium and oxygen is 2 8 3 and 2 6 respectively. So, to complete their valence shell aluminium has to give 3 electrons and oxygen has to take 2 electrons. But, there are 2 atoms of aluminium and three atoms of Oxygen. Now, tell me that how these elements become neutral? How these elements give and take electrons?