Ionization energies describe how unwilling an atom is to lose an electron, and electron affinities measure how eager a neutral atom is to add one more electron. Both of these quantities describe the attraction of an atom for an electron under special conditions. Electronegativity is a more general measure of the attraction of an atom for an electron in bond-forming situations.

Electronegativities could be calculated from ionization energies and electron affinities, but in practice they are obtained by measuring the strengths of different types of bonds in molecules.

Robert Mulliken and Linus Pauling independently devised the electronegativity concept. In the Pauling electronegativity scale, the electron-losing lithium atom is assigned an electronegativity (or EN) of 1.0, the electron-grabbing fluorine is given an EN of 4.0, and the other atoms are assigned intermediate values, as shown on the next page. In a bond between two atoms, the electrons will be attracted more strongly to the atom with the greater electronegativity.