The electronegativity of an element is a measure of power of the element to attract electron to itself in chemical compounds. It is difficult to assign accurate electronegativities to elements, partly because the precise values may vary in different compounds. Our quantitative estimation of electronegativity is the average of ionization energy and the electron affinity for an element in eV. It is known as Mulliken’s scale. The trends in electronegativity values are similar to those in ionization  energies. Various measures of electronegativity have been proposed and all give roughly parallel scales. Pauling scale is based upon excess bond energies; Alfred and Rochow’s (R/A) is based upon effective nuclear charges. The % age of ionic character in a bond can be estimated by finding the differences in electronegativity values of atoms forming the bond. The % age ionic character and difference in electronegativity values are given below : 

Electronegativity difference	% age ionic character
1.0	20%
1.5	40%
2.0	60%
2.5	80%

Pauling and Mulliken values of electronegativity are related as $X_{\text{Pauling }}=0.336\left[X_{\text{Mulliken }}-0.615\right]$