According to the University of Waterloo, chemical formulas are categorized into empirical, molecular and structural formulas, which display the chemical of interest in distinct ways. Empirical formulas use the ratio of atoms to describe the chemical of interest, while the molecular formulas use the actual number of atoms in the molecule.
The University of Wisconsin-Madison illustrates the difference between empirical and molecular formulas by using butene. Butene has four carbons for every eight hydrogens, so the molecular formula of butene is C4H8. The empirical formula is based on the ratio of the atoms; in butene, for every carbon atom, there are two hydrogen atoms. The empirical formula of butene is, therefore, CH2.
Structural formulas, according to the University of Waterloo, display how atoms are bonded in a molecule or an ion. The structural formula of ethanol is CH3CH2OH. Structural formulas use repeated chemical symbols to show the location of the atoms in a molecule. For example, in ethanol, three hydrogen atoms surround the first carbon, while two hydrogen atoms surround the second carbon.
Whether they are empirical, molecular or structural, chemical formulas consist of symbols and subscripts describing the amount of atoms present. The location or ratio of the subscripts distinguishes the types of chemical formulas.