Question

A certain ionic compound is made entirely of aluminum and oxygen. part a what is the formula for this compound?

Answer 1

It is Al₂O₃;
The ion of Al is Al³⁺;
The ion of O is O²⁻;
Balance out the charges:
2(Al³⁺) = 6+ charge
3(O²-) = 6- charge
They cancel out;
Now, just put the coefficients in front of their respective ions to get:
Al₂O₃