The term formula in chemistry can have a variety of meanings. The empirical formula of a compound is that which is obtained through laboratory research. By analyzing the chemical composition of a compound in the laboratory and knowing the atomic weights of the elements in the compound, one can calculate the simplest, or empirical, formula for that compound. For example, the analysis of ethane shows that the ratio of carbon to hydrogen atoms in the molecule is 1: 3. Therefore, the empirical formula for ethane, is CH₃.

If one also knows the molecular weight of a compound, the molecular formula for that compound can be determined. Knowing the molecular weight of ethane to be 30, for example, allows one to calculate the molecular formula for the compound to be C₂H₆.

Finally, the structural formula of a compound shows not only the kind and actual number of atoms, but...