In Pauling’s scale electronegativities are calculated from the bond energies.
 ${\chi }_A-{\chi }_B=0.208\sqrt{\Delta }$
 $\Delta$ is excess bond energy (Resonance energy)
= Actual bond energy - bond Energy of 100% covalent bond.
 $\to$ 100% covalent bond energy $(\text{A}-\text{B})$ is the geometric mean of the covalent bond energies of  $\text{A}-\text{A}$ and  $\text{B}-\text{B}$  molecules.
 $$\begin{gathered} {\text{E}}_{100\%}\text{\hspace{0.17em}covalent}=\sqrt{{\text{E}}_{\text{A}-\text{A}}\times {\text{E}}_{\text{B}-\text{B}}} \\ \Delta ={\text{E}}_{\text{A}-\text{B}}-\sqrt{{\text{E}}_{\text{A}-\text{A}}\times {\text{E}}_{\text{B}-\text{B}}} or {\text{E}}_{\text{A}-\text{B}}=\frac{1}{2}[{\text{E}}_{\text{A}-\text{A}}\times {\text{E}}_{\text{B}-\text{B}}] \\ {\chi }_{\text{A}}-{\chi }_{\text{B}}=0.208{[{\text{E}}_{\text{A}-\text{B}}-{({\text{E}}_{\text{A}-\text{A}}\times {\text{E}}_{\text{B}-\text{B}})}^{\raisebox{1ex}{$1$}\!\left/ \!\raisebox{-1ex}{$2$}\right.}]}^{\raisebox{1ex}{$1$}\!\left/ \!\raisebox{-1ex}{$2$}\right.} \end{gathered}$$

(When E is in Kcals/mole)
In SI units (E is in KJ/mole)
${\chi }_{\text{A}}-{\chi }_{\text{B}}=0.1017\sqrt{\Delta }$

reference element is H. 
For a diatomic hetero molecule

Bond length, (l) 

 $l=r_A+r_B-0.09(X_A-X_B)$
Where,  $X_A=$ Electronegativity of more electronegative atom
$X_B=$  Electronegativity of less electronegative atom