chemistry question????

Question

4Al + 3O₂ → 2Al₂O₃

How does 4Al+3O₂ turn into 2Al₂O₃? WHat type of dividing is going on? Shouldn't it be 4Al3O₂? (the original problem was to make Al+O₂ into a balaced equation, and I understood it until that last part.)

Answer 1

Each atom of Al forms an ion  with a charge of 3+.

 

Each O has a charge of 2-.

 

Therefore, 2 Al cations will combine with 3 O anions to make one formula unit of Al2O3.  You get 2 of these formula units when you balance the equation which accounts of the law of conservation of mass.