# Formula of Manganese (IV) Ion

When determining the formula of manganese (IV) oxide, since it’s made up of $\ce{Mn^4+}$ and $\ce{O^2-}$ ions, why is the formula $\ce{MnO2}$ and not $\ce{Mn2O4}$?

Any help would be greatly appreciated

• Both are right, but MnO2 is simpler. Jun 17, 2018 at 18:57
• Good question, be careful what do you mean is it solid MnO2 or manganese(VI) oxide in the gas form. I have no idea if manganese (VI) oxide can form a gas but I know that chromium(VI) oxide in the gas state is in fact Cr3O9 rather than CrO3 Jun 17, 2018 at 20:37

For ionic compounds there is really no such thing as a "molecule" of the compound. In the solid state the ions exist in a 3D crystalline structure and there is no unique way to associate a particular $\ce{Mn^{4+}}$ ion with a particular pair of $\ce{O^{2-}}$ ions. Therefore the simplest integer ratio is used as the "molecular formula."
To get a proper formula, the ionic charges have to neutralize, so $\ce{1 Mn^4+}$ ion neutralizes $\ce{2 O^2-}$ ions.