Molecular Formula

The molecular formula is the actual number of atoms of each element in a molecule.It is always a whole-number multiple of the empirical formula. For example, butane has the molecular formula C₄H₁₀ and the empirical formula C₂H₅.To find the molecular formula, you need the empirical formula and the relative molecular mass, M_r. Divide M_r by the empirical formula mass to find the multiplier.Example: a compound has the empirical formula CH₂ and M_r = 56.0. The empirical formula mass is 12.0 + 2.0 = 14.0. 56.0 / 14.0 = 4, so the molecular formula is C₄H₈.The M_r is often found from the molecular ion peak in a mass spectrum.