Zinc nitrate, "Zn(NO"_3)_2"Zn(NO3)2, is an ionic compound. Ionic compounds do not form molecules. Ionic compounds exist as crystal lattices. The lowest whole number ratio, also the empirical formula, represents a formula unit. The expression "5 Zn(NO"_3)_2"5 Zn(NO3)2 represents 5 formula units or 5 moles of zinc nitrate.