For covalent substances, the formula represents the numbers and types of atoms composing a single molecule of the substance; therefore, the formula mass refers to a molecular mass. Consider chloroform (CHCl₃), a covalent compound once used as a surgical anesthetic and now primarily used in the production of tetrafluoroethylene, the building block for the “anti-stick” polymer, Teflon. The molecular formula of chloroform indicates that a single molecule contains one carbon atom, one hydrogen atom, and three chlorine atoms. The average molecular mass of a chloroform molecule is, therefore, equal to the sum of the average atomic masses of these atoms.