Electronnegativity is the attractive force of an element fora shared pair of electrons in a molecule. When two different kinds of atoms share a pair of electrons, one atom assumes a parital positive charge and the other a partial negative charge with respect to each other. This difference in change occurs because the two atoms exert unequal attraction for the pair of shared electrons. For example, both hydrogen and fluorine need one electron to form table electron configuration. They share a pair of electrons in hydrogen fluoride, HF. Fluorine is more electronegative and therefore has a greater attraction for the shared electrons than does hydrogen. As a result, the pair of electrons is displaced towrard the fluorine atom, giving it a parital negative charge. It should be understood that the electron is not transferred entirely to the fluorine atom, as in the case of sodium fluoride, and no ions are formed. A partial charge is usually indicated by the Greek letter delta, Thus, a partial positive charge is represented by delta+ and a partial negative charge by delta-

Electronnegativitiy, or the ability of an atom to attract an electron, depends on the following: (a) the number of shells shielding the nucleus from the outer-shell electrons (b) the charge of the nucleus, and (c) the distance of the outer electrons from the nucleus. A scale of relative electronegativities, in which the most electronegative element, fluorine, is assigned a value of 4.0, was developed by the Nobel  Laureate (1954 - 1962) Linus Pauling. The relative electronegativity of the nonmetals is high and that of the metals is low. These electronnegativities indicate that atoms of metals have a greater tendency to lose electrons than atoms of nonmetals and that nometals have greater tendency to gain electrons than metals. The higher the electronnegativity, the greater the attraction of electrons.