Why Fluorine has more electronegativity than Chlorine although Chlorine has more electron affinity/pull for the electrons than Fluorine ?
The question is fairly good. One might expect that if Chlorine has more pull for electrons(tendency to gain electrons) than Fluorine then it should also have more tendency to gain the shared pair of electrons of the covalent bond. But this is not true and the reason for so is explained as follows:- Let us consider the molecule AーB in which A and B are bonded covalently. I must remember you that there are two electrons present in the bond pair which are in turn of two different origin, one comes from A and other comes from B. Now electronegativity is the tendency to attract (or gain) both the electrons of the bond pair. The attraction here is for 2 different electrons, one is of the other atom's and one is of own's atom. The strength of the pull for the 2 electrons of different origin will depend upon 2 different respective factors. The pull for the electron of the other atom will depend upon the electron affinity of the pulling atom, higher the affinity stronger will be the