Abstract: The methods of weighed atomic sums were suggested on the basis of binary code of molecular periphery for the descriptions of atomic asymmetric environments. The weighed atomic sum of an atom is a measure of the asymmetry of the atomic environment as obtained by circulating around the molecule going in opposing directions, and so the weighed atomic sum of an atom in a molecule and that of corresponding atom in the opposite enantiomer are of the same magnitude but of the opposite sign. Weighed atomic sums were available in not only chiral molecule, but also achiral molecule. Compared with atomic sums approached by Randic′, weighed atomic sums are more distinctive and better than atomic sum to represent atomic asymmetry.

Key words: Benzenoids, 2D molecular shape, Atomic asymmetry, Weighed atomic sum