Thus, a formula is a symbolic representation of one molecule of the substance which tells the number and kinds of atoms of various elements present in its molecule.
The determination of the formula of a substance involves first the determination of its 'Empirical Formula' and then the 'Molecular Formula'.
Empirical irical Formula: The empirical formula of a compound is the chemical formula which expresses the simplest whole number ratio of the atoms of the various elements present in one molecule of the compound.
For example, the empirical formula of benzene is CH, that of hydrogen peroxide is HO and that of glucose is CH2O. This suggests that in the molecule of benzene, one carbon atom is present for every one hydrogen atom ; in the molecule of hydrogen peroxide, one atom of hydrogen is present for every one oxygen atom, and in the molecule of glucose, one atom of carbon is present for every one atom of oxygen and two atoms of hydrogen. Thus, the empirical formula of a compound represents only the atomic ratio of the various elements present in its molecule.
Molecular Formula: The molecular formula of a compound is the chemical formula which represents the true formula of its molecule. It expresses the actual number of atoms of various elements present in one molecule of the compound.
For example, the molecular formula of benzene is C6H6, that of hydrogen peroxide is H2O2 and that of glucose is C6H12O6. This suggests that one molecule of benzene contains six atoms of carbon and six atoms of hydrogen, one molecule of hydrogen peroxide contains two atoms of hydrogen and two atoms of oxygen and one molecule of glucose contains six atoms of carbon, twelve atoms of hydrogen and six atoms of oxygen.