## Chemistry and Chemical Reactivity (9th Edition)

$CoO$ $Co_2O_3$
The oxide ion is $O^{2-}$. For $Co^{2+}$: Both have the same charge, so $CoO$ For $Co^{3+}$: To balance the charges we need 3 $O^{2-}$ and 2 $Co^{3+}$: $Co_2O_3$