An empirical formula represents the simplest atomic ratio of a chemical compound. These formulas may not represent the actual number of atoms in a compound, but they do indicate all the elements present.
Empirical formulas are closely related to molecular formulas. Molecular formulas show the actual number of atoms for each element present in a compound. Consider the compound acetylene, which is made of carbon and hydrogen atoms. The empirical formula for acetylene is CH, whereas the molecular formula is C2H2, as there are two atoms of each element. Different compounds can have the same empirical formula but different molecular formulas.