What is electronegativity?

Explanation

Electronegativity: ..The tendency of the atom of an element to attract the shared electron pair(s) more towards itself in a hetronuclear diatomic molecule or in a polar covalent bond...
Measuring electronegativity Pauling scale: Pauling scale is based on the values of bond energy. The bond energy of a compound A-B is the average of bond energies of A-A and B-B molecules.
`E_(A-B)= (1)/(2) (E_(A-A) + E_(B-B))`
But the experimental values of `E_(A-B)` is found to exceed the theoretical value. The difference is `Delta`.
`therefore Delta = E._(A-B) -E_(A--B)`
`Delta` indicates the polarity of the covalent bond. It is measured in k. cal. `mol^(-1)`. Pauling gave the relation `X_(A)-X_(B)=0.208 xx sqrtDelta`
In S.I. units `X_(A)-X_(B)= 0.1017 sqrtDelta` where `Delta` is measured in kJ/mole
`X_(A) and X_(B)` are the electronegativities of A and B. Pauling arbitrarily fixed 2.1 as the electronegativity value of Hydrogen and calculated the electronegativities of other elements. On Pauling scale Fluorine has the highest EN value 4.0.
From the values of the electronegativity of elements, the nature of the chemical bond formed can be understood. If two bonded atoms differ by 1.70 or more ion their EN values, the bond between them would be either 50% or more than 50% ionic in nature. Similarly if the difference in the EN values of the atoms is less than 1.70, the bond formed is more than 50% covalent in nature.