Why is the Electronegativity difference for atoms in bonding uncertain while determining what the compound will be?
According to the IB(International Baccalaureate) they say that the Electronegativity difference required for Ionic bonds is 1.7 though compounds like Hydrogen Fluoride are covalent even though they have a Electronegativity difference of 1.9. If the IB scale of above 1.7 being ionic and below 1.7 being covalent then why are there many exceptions to this rule? Also, why does Electronegativity not change, since having more electrons in atom would probably cause repulsion of new electrons? If you search for what the Electronegative difference to predict bonding and were to look at Yahoo.answers you will see 3 different answers to how to predict these reactions at 1.7,1.8 or 1.9 electronegative difference Yahoo question. Another exception is Calcium Carbide which forms a ionic bond at 1.5 electronegative difference.