How is it possible to identify so many different chemical compounds and tell them apart? There is a database that keeps track of them and is updated daily to include compounds that exist in nature or that have been synthesized in the lab. This investigation focuses on determining chemical formulas.
The composition of a chemical compound, or what it is made of, can be described at least three different ways. The percent composition gives the percent by mass and is the simplest way experimentally to describe the composition of a substance. It tells what elements are present and their mass ratio. It is more interesting, however, and more informative to know how many atoms of each kind of element combine with one another. Since all the atoms of a given compound have the same average atomic mass, the elements in the compound exist in a fixed whole-number ratio. This ratio is the empirical formula. Empirical means experimentally determined. An additional experiment can be performed to determine the molecular formula. For example, finding the molecular mass would allow the molecular formula to be calculated.
The organic compounds acetylene and benzene, for example, have the same empirical formula, CH - one hydrogen atom for every one carbon atom. The two compounds have different molecular formulas - C2H2 and C6H6. Notice that in both cases, the molecular formula is a simple multiple of the empirical formula. The molecular formula of a compound tells us the actual number of atoms in a single molecule of a compound.