Abstract: Here in this study it is shown that the numerical values of local softness on C in CH₄, CH₃F, CH₂F₂, CF₃H and CF₄; on N in NH₃, NH₂F, NHF₂ and NF₃; and on B in BH₃, BH₂F, BHF₂ and BF₃ tend to decrease from the first member in each series to the last one on successive substitution of H atom by hard electronegative F atom. Thus the symbiotic phenomenon is nicely reflected in the present study. Again, the energy partitioning study shows that on substitution of H atom in each series by electronegative F atom the electronic charge densities on central atoms (C, N and B in series I, series II and series III respectively) decrease. As a result of which the numerical values of electron-electron repulsion parameter on those central atoms decrease gradually and this tendency makes the electrons on the aforesaid central atoms gradually less destabilizing. So the electrons on the central atoms become gradually hard to ionize on gradual replacement of H atom by F atom in each series leading to the gradual decrease of softness values on those central atoms.


KEY WORDS: Symbiosis, local softness, energy partitioning, fukui functions.