Question

Explain Pauling's scale of electronegativity.

Answer 1

Pauling's scale is based on an empirical relation between the energy of a bond and the electronegativity of bonded atoms.
Consider a bond A-B between two dissimilar atoms A and B of a molecule AB. Let the bond energies of A-A, B-B and A-B bonds be represented as $E_{A-A},E_{B-B}$ and $E_{A-B}$ respectively. It may be seen that the bond dissociation energy of A-B is almost higher than the geometric mean of the bond dissociation energies of A-A and B-B bonds i.e., $E_{A-B}>\sqrt{E_{A-A}\times E_{B-B}}$
Their difference $\left(\Delta \right)$ is related to the difference in the electronegativities of A and B according to the following equation.
$\Delta =E_{A-B}-\sqrt{E_{A-A}\times E_{B-B}}$
$=(X_A-X_B{)}^2$
$0.208\sqrt{\Delta }=X_A-X_B$
Here, $X_A$ and $X_B$ are the electronegativities of A and B respectively. The factor $0.208$ arises from the conversion of Kcals to electron volt. Considering arbitrarily the electronegativity of hydrogen to be $2.1$, Pauling calculated electronegativities of other elements with the help of this equation.
The disadvantage of Pauling scale:
The disadvantage of Pauling's scale is that bond energies are not known with any degree of accuracy for many solid elements.