Electronegativity Scales Essay

951 Words4 Pages
ELECTRONEGATIVITY SCALES Electronegativity scale is an arbitary scale. They are based on various types of experimental data like bond energy, dipole moment, ionisation potential and electron affinity. Most commonly used scales are 1. Pauling’s scale 2. Mulliken’s scale 3. Sanderson’s scale 4. Alfred and Rochow’s scale Pauling’s scale (1932) This scale is based on an empirical relation between the energy of a bond and the electronegativities 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 EA-A, EB-B and EA-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., A B A A B B E E E − − − > ⋅ Their difference (⊗) is related to the difference in the electronegativities of A and B according to the following equation A B A A B B E E E − − − ⊗ ’ − ⋅ 2 A B ’ (X −X ) (or) 0.208 ⊗ = XA – XB Here, XA and XB are the electronegativities of A and B respectively. The factor 0.208 arises from the conversion of Kcals to electron volt. Considering arbitarily the electronegativity of hydrogen to be 2.1, Pauling calculated electronegativities of other elements with the help of this equation. 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. Problem Calculate the electronegativity of chlorine from the following data EH-H = 104 K cal mol-1 ; ECl-Cl = 36 K cal mol-1 EH-Cl= 134 K cal mol-1 According to Pauling’s equation HCl H H Cl Cl _ E E − E − ’ − ⋅ _ ’ 134 − 104⋅36 = 134 – 61.18 = 72.82 Cl H 0.208 _ ’ X −X X X 0.208 72.82 Cl H ⇒ − ’ = 1.77 XCl - 2.1 = 1.77 [ XH = 2.1] XCl = 1.77 + 2.1 = 3.87 2. Mulliken’s Scale In

More about Electronegativity Scales Essay

Open Document