A chemical formula is an expression that shows the elements in a compound and the relative proportions of those elements. A molecular formula is a chemical formula of a molecular compound that shows t...A chemical formula is an expression that shows the elements in a compound and the relative proportions of those elements. A molecular formula is a chemical formula of a molecular compound that shows the kinds and numbers of atoms present in a molecule of the compound. An empirical formula is a formula that shows the elements in a compound in their lowest whole-number ratio.