any of several kinds of expressions of the composition or structure of chemical compounds. The forms commonly encountered are empirical, molecular, structural, and projection formulas., the molecular or the empirical formula of a compound consisting of discrete molecules, a notation utilizing chemical symbols and numbers to indicate the chemical composition of a pure substance; examples are CH4 for methane and HCl for hydrogen chloride., elementide sümboleist koosnev avaldis, millega märgitakse keemilise ühendi kvalitatiivset ja kvantitatiivset koostist