It speaks of relative numbers. For example, CH 2 says that there will be twice as many Hydrogens as there are carbons in the compound that has this simplest formula. It does not address how many exact numbers of Hydrogens and Carbons there will be in the compound. A formula whose subscripts represent the absolute exact numbers of atoms of each element per molecule of the compound or the absolute number of moles of each element per mole of the compound. A molecular formula may be reducible to a simple formula if all its subscripts are divisible by a common denominator.
Some compounds have the same empirical and molecular formula.
For example, Carbon Dioxide has as its empirical and molecular formula CO 2 . The empirical and molecular formula for Sulfur Dioxide are the same SO 2 . There are many situations where two or more compounds have the same simplest formula, but differ by their molecular formulas. 6 H 6 and acetylene's molecular formula is C 2 H 2 . Return to the top of the page.