Electronegativity is a measure of the ability of an atom to attract and hold electrons. Robert Mulliken suggested that electronegativity could be expressed essentially as an average of the ionization potential and the electron affinity of the atom. The ionization potential is the minimum amount of energy necessary to remove an electron completely from the outer electron shell of an atom. The electron affinity is the energy given off when a neutral atom acquires an electron.Linus Pauling proposed a somewhat different approach for determining electronegativies, but the values calculated by the two methods are in good agreement.

Atoms with widely different electronegativities will form ionic bonds, since the atom with the highest eletronegativity is able to pull an electron away from the atom with the lower electronegativity. For atoms whose electronegativity difference is not large, the atom with the higher electonegativity is not able to pull an...