Chemical Bond - Electronegativity

The term that Pauling developed for this concept is electronegativity. Electronegativity is, in a general sense, the tendency of an atom to attract the electrons in a covalent bond. The numerical values for the electronegativities of the elements range from a maximum of 4.0 for fluorine to a minimum of about 0.7 for cesium. A bond formed between fluorine and cesium would tend to be ionic because fluorine has a much stronger attraction for electrons than does cesium. On the other hand, a bond formed between cobalt (electronegativity = 1.9) and silicon (electronegativity = 1.9) would be a nearly pure covalent bond since both atoms have an equal attraction for electrons.

The modern concept of chemical bonding, then, is that bond types are not best distinguished as purely ionic or purely covalent. Instead, they can be envisioned as lying somewhere along a continuum between those two extremes. The position of any particular bond can be predicted by calculating the difference between the two electronegativities of the atoms involved. The greater that difference, the more ionic the bond; the smaller the difference, the more covalent.