Empirical formula

Empirical formula
The empirical formula of a molecule is a simpler formula than the molecular formula. It is useful when scientists know only the ratio of atoms in a compound, for example, after performing a chemical analysis that reveals the weight of each element in the compound. The empirical formula looks similar to the molecular formula, but the subscripts only include information on the ratios of the elements with respect to each other and not on the actual number of atoms. For example, ethane’s molecular formula is C2H6, which shows that the ratio of carbon atoms to hydrogen atoms is 1 to 3, so its empirical formula is CH3. An unknown sample with the empirical formula CH3 may be ethane, but it cannot be butane, which has an empirical formula of C2H5. Water’s molecular formula is the same as its empirical formula, H2O. Molecular formulas always have subscripts that are whole number multiples of the empirical formula of a compound. Chemists also use empirical formulas for ionic compounds.