Empirical Formula and Molecular Formula

Once you know the elements present in a compound and their mass percentages (from experimental elemental analysis), you can work backwards to the compound's formula. Two related but distinct formulas describe a compound:

• The empirical formula is written using the simplest whole-number ratio of the different atoms present in one molecule, as subscripts on each atomic symbol.
• The molecular formula is written using the actual number of each type of atom present in one molecule. …