Covalent radius of 82 Pb is 1 . 53 A o . Calculate its electronegativity at the Alfred-Rochow scale:

Alfred-Rochow scale of electronegativity measures the electrostatic force of attraction, acting between the nucleus and the valence electrons of an atom. The most electronegative atom is fluorine. The Alfred-Rochow scale of electronegativity ( χ ) for an element is given by the formula: χ AR = 0 . 744 + 0 . 359 × Z eff r 2 . where, Z eff is the effective nuclear charge acting on the valence electrons; r is the covalent radius of the atom. The formula for the effective nuclear charge is given as: Z eff = Atomic Number ( Z ) - Shielding Factor ( σ ) . If n is taken as the ultimate shell, and ( n - 1 ) is taken as the penultimate shell, then the rules for calculating the effective nuclear charge according to Slater's rule, go as follows: The shielding factor of ns and np electrons is 0 . 35 each. The shielding factor of ( n - 1 ) s and ( n - 1 ) p electrons is 0 . 85 each. The shielding factor of lower shell s and p electrons is 1 . 00 each. The shielding factor of nd and nf electrons is 0 . 35 each. The shielding factor of all the lower shell electrons is 1 . 00 each. The electronic configuration of Pb 82 is: 1 s 2 , 2 s 2 2 p 6 , 3 s 2 3 p 6 3 d 10 , 4 s 2 4 p 6 4 d 10 4 f 14 , 5 s 2 5 p 6 5 d 10 , 6 s 2 6 p 2 . Total number of s and p electrons in the 6 th ( nth ) shell = 4 . ⇒ Screening factor = 4 × 0 . 35 = 1 . 4 . Total number of s and p electrons in the 5 th [ ( n - 1 ) th ] shell = 8 . ⇒ Screening factor = 8 × 0 . 85 = 6 . 8 . Total number of lower shell s and p electrons = 26 . ⇒ Screening factor = 1 . 00 × 26 = 26 . Total number of d and f electrons in the 6 th ( nth ) shell = 0 . Total number of d and f electrons in the lower shells = 44 . ⇒ Screening factor = 1 . 00 × 44 = 44 . ∴ Total screening effect of all the electrons in an atom of Pb = 1 . 4 + 6 . 8 + 26 + 44 = 78 . 2 . Z eff = 82 - 78 . 2 = 3 . 8 . The value of r is given as 1 . 53 A o . Putting the values in the Alfred-Rochow scale, we get: ∴ χ Pb AR = 0 . 744 + 0 . 359 × 3 . 8 ( 1 . 53 ) 2 = 1 . 32 . When the difference in the electronegativity between the two atoms increases, then the polarity of the bond also increases.