The molecular formula specifies the actual number of atoms of each element in a molecule.

The conventional form for writing a molecular formula is to write the symbol for each element followed by a subscript, indicating the actual number of those atoms present in a molecule. When only one atom of an element is present, the subscript is omitted. For example, the molecular formula for water, H₂O, specifies that there are two hydrogen atoms and one oxygen atom present in each molecule of water.

It is important to remember that the molecular formula—in contrast to the simpler empirical formula that specifies only the relative number of atoms or moles present in a compound--identifies the actual number of atoms present in a molecule. For example, the molecular formula for glucose (a sugar important in many biological reactions), C₆H₁₂O₆ specifies that in each...