Question

Mention the disadvantage of Pauling and Mulliken scale.

Answer 1

Both Mulliken and Pauling Electronegativity is a measure of the electron attraction power of an atom in a molecule. According to the Pauling formulation, it was described as a thermodynamic property, which relate to the bond energy of the molecule. The difference in the bond energy of any molecule, A-B from the average of A-A and B-B bond energies is a measure of the electronegativity difference between A and B. In other words, if χA and χB, are the electronegativity of atom A and B, then,      The factor 0.102 is a conversion factor between kJ/mol and eV. The factor (eV)-1/2 is added just to make electronegativity, a dimensionless quantity. Pauling arbitrarily chose a value of 2.1 for the electronegativity of H atom. The EN values for other atoms were found relative to this. Thus Pauling scale is not an absolute scale of electronegativity. Another scale, which is introduced by Mulliken, is based on the properties of atoms. An atom with high ionization energy and high electron affinity is less likely to loss an electron, while it is bonded to another atom, whereas it is more likely that it will gain electrons and hence may be called highly electronegative. Thus Mulliken expressed EN as the average of ionization energy (IE) and electron affinity (EA); in the actual calculation, the valence state IE and EA (IEv and EAv) are used instead of the normal IE and EA, to account for the effect of other atoms bonded to the atom under consideration (The calculation of IEv and EAv is slightly complicated and hence will not be discussed here). Thus, the Mulliken EN can be expressed as:   A conversion of the Mulliken EN to the units of the Pauling EN is:                   It should be noted that Xp in the above equation is not Pauling electronegativity. It is Mulliken electronegativity Xm converted to Pauling units.

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Answer 2

Answer:

Both Mulliken and Pauling Electronegativity is a measure of the electron attraction power of an atom in a molecule. According to the Pauling formulation, it was described as a thermodynamic property, which relate to the bond energy of the molecule. The difference in the bond energy of any molecule, A-B from the average of A-A and B-B bond energies is a measure of the electronegativity difference between A and B. In other words, if χA and χB, are the electronegativity of atom A and B, then,      The factor 0.102 is a conversion factor between kJ/mol and eV. The factor (eV)-1/2 is added just to make electronegativity, a dimensionless quantity. Pauling arbitrarily chose a value of 2.1 for the electronegativity of H atom. The EN values for other atoms were found relative to this. Thus Pauling scale is not an absolute scale of electronegativity. Another scale, which is introduced by Mulliken, is based on the properties of atoms. An atom with high ionization energy and high electron affinity is less likely to loss an electron, while it is bonded to another atom, whereas it is more likely that it will gain electrons and hence may be called highly electronegative. Thus Mulliken expressed EN as the average of ionization energy (IE) and electron affinity (EA); in the actual calculation, the valence state IE and EA (IEv and EAv) are used instead of the normal IE and EA, to account for the effect of other atoms bonded to the atom under consideration (The calculation of IEv and EAv is slightly complicated and hence will not be discussed here). Thus, the Mulliken EN can be expressed as:   A conversion of the Mulliken EN to the units of the Pauling EN is:  It should be noted that Xp in the above equation is not Pauling electronegativity. It is Mulliken electronegativity Xm converted to Pauling units.