A certain ionic compound is made entirely of aluminum and oxygen.
Chemical formulas indicate the ratios of the different types of atoms in a compound. Percentage composition indicates the relative masses of each element in a compound. Mass ratios are important for lab work, and atomic ratios are important for understanding chemical reactions.
Aluminium Oxide: Al2O3
Al3+ .............. O2-
When they bond: It is ionic as it takes place by the transfer of electrons from Aluminium(metal) to Oxygen(Non-metal). Hence, the bond is:
Al2O3, Aluminium Oxide or alumina.