In this paper, we define a novel valence of vertex for hetero-atoms used in molecular topology. The novel valence of vertex can unify the form of vertex valence of various atoms, have explicit physical meanings, and show linear relationship with Mulliken electronegativities. By using the novel index of vertex, different oxidation states for the same atom can be distinguished. We have also generalized the valence and non-valence indexes to hetero-atoms. Results show that this new index keeps all information of the molecular connectivity method but is superior in dealing with th electronic-properties of molecules.

Key words: HETEROATOM, SUBSTITUENT EFFECT