# Is there a technique to determine the chemical formula of an ionic compound?

Sep 15, 2017

Yes. The technique is called the crisscross rule. The number (size) of the charge on one ion becomes the subscript for the other ion.

#### Explanation:

${\text{Na}}^{+}$ + ${\text{O}}^{2 -}$$\rightarrow$$\text{Na"_2"O}$
${\text{Fe}}^{3 +}$ + ${\text{O}}^{2 -}$$\rightarrow$$\text{Fe"_2"O"_3}$