Debate on Pauling Electronegativity Confusion

Yonghe Zhang

American Huilin Institute

 

Linus Pauling was awarded the Nobel Prize in chemistry for proving a link between electronegativity and the chemical bond. Pauling defined electronegativity in 1932 as the power of an atom in a molecule to attract electrons to itself [1]. The concept could be considered as an approximation of intuitively understanding the chemical bond strengths. However, the definition is not an unambiguous for the valence states [2-8]. And Pauling electronegativity scales, which based on much less a direct way of description by spectroscopy, unconditionally used and extended the limited situation of the linear difference of the thermochemical energy of two elements (H and Cl) to the all elements. And so that would inevitably mislead to the opposite wrong results [9-11].

 

Over the years, the attempts to derive a comprehensive quantitative scale of electronegativity have been disappointed because the lack of correlation between the experimental quantities and scale over a wide range of the electron quantum configurations.

 

 

In 1981-1982, on the basis of Bohr energy model,


                                              
E = - Z2me4/8n2h2ɛ02 = - RZ2/n2


Author obtained the effective principal quantum number n* and the effective quantum nuclear charge Z* from the ionization energy [2,3]
 

                                                              Z*=n*(Iz/R)½

Then the first scale of electronegativity in different valence states on spectroscopy corresponding quantum electron configurations of the orbital from 1s to nf  was proposed [2,3]:

                                               
Xz = 0.241 n*( Iz /R) ½rc-2 + 0.775


where
Iz is the ultimate ionization energy for outer electrons of the s, p, d and f orbital of the atom. R is the Rydberg constant, R = 22µ42e4/h2 = 13.6 eV, h is Planck’s constant and Z*=n*(Iz/R)½ is the effective nuclear charge Z* felt by the valence electron at the  covalent boundary r.

 

Built-up the various quantum parameters of the atomic orbital Iz(s,p,d,f), n*,Z*, rc , rc-1 , n*rc-1 , based on spectroscopy, the electronegativity  Xz formed a Method of the multiple-functional prediction, which can explain chemical observations of elements of all orbital electron configurations from 1s to nf, including the σ-bond, the linear or nonlinear combinations of ionic bond and covalent bond, the orbital spatial overlaps and the orbital spatial crosslinks. Therefore, this is what have been expected orbital ionization energy electronegativity that best meets Bergmann-Hinze criterion [5] and the Cherkasov conclusion [6].

 

After the above electronegativity published the author received hundreds of appreciation cards and letters. Henry Taube, Nobel Laureate, wrote in his letter: "Electronegativity continue to be a useful concept, and becomes even more useful when it is treated as a function of oxidation state." [12}. Mackay et al. pointed out that the major difficulty in Pauling's electronegativity is that the attraction for an electron is clearly not expected to be the same for different valencies of an element [8] and they encompassed in their university textbook the Zhang electronegativity in valencies.

 

But Pauling was still in confusion and continued to maintain his ambiguous valence state [13]: “I must say that I am not able to form a reliable opinion about the value of your work. I note that for a number of the elements your calculated values are close to my values of the electronegativity, and also that for other elements there is a considerable deviation. I suggest that you might discuss some property of the elements, in various compounds, and in different valence states, in order to find out whether or not your values are helpful in understanding the properties”.

 

To reply Pauling's concerns, the author published two papers “Electronegativities of elements in valence states and their applications” and “A scale for strengths of Lewis acids” [14], wherein 126 metal ion Lewis acids, in various compounds, and in different valence states, are calculated from:

 

                                                  Z = z/r2 - 0.77 Xz + 8.0

Where 
Xz is Zhang electronegativity in valence states and z is the charge number of the atomic core (the number of valence electron). Z is Lewis acid strength. The Z values give a quantitative scale of the relative Pearson hardness or softness for various Lewis acids and agree fairly well with the Pearson classification [15] and the previous work [16-18] (Lewis Acid Strength Table).

From which Zhang ionocovalent theory is established [4,7]. The Zhang Lewis acid strengths Z, the Brown Lewis acid strength Sa, Portier ICP, Lenglet’s RP Relationship, “Electron-acceptor-Strength”, Scattering Cross Section Q and more applications are derived from Zhang electronegativity which has been widely quantitatively used over 30 years, forming an international school [19 (
International Ionocovalency Schools -)]

 

The new papers not only satisfactorily replied Pauling’s concerns, but also give the author the conditions to develop the new theory that everything exists in Ionocovalency, theionic energy harmonized with the covalent environmentthat correlates with quantum potential and spectroscopy [9]

 

I(Z*)(n*rc-1) = Ze2/r = n*(Iz/R)½ rc-1

 

We had not received Pauling’s any review again and don’t know if Pauling had no more confusions? But we do know somewhere is still in confusion.


References


[1] Pauling, L. J. Am. Chem. Soc. 1932, 54, 3570.

[2] Zhang, Y. J. Molecular Science 1 (1981) 125.
[3] Zhang, Y. Inorg Chem. 21 (1982) 3886.
[4] Portier, J.; Campet, G.; Etoumeau, J. and Tanguy, B. Alloys Comp.,1994a, 209, 59-64.

[5] D. Bergmann and J. Hinze. Angew, Chem. Int. Ed. Engl. 1996, 35, 150-163.

[6] A. R. Cherkasov, V. I. Galkin, E. M. Zueva, R. A. Cherkasov, Russian Chemical Reviews, 67, 5 (1998) 375-392.
[7] Lenglet, M. Iono-covalent character of the metal-oxygen bonds in oxides: A comparison of experimental and theoretical data. Act. Passive Electron. Compon.2004, 27, 1–60.

[8] Mackay, K. M.; Mackay, R. A.; Henderson W. "Introduction to Modern Inorganic Chemistry", 6th ed., Nelson Thornes, United Kingdom, 2002, pp 53-54.
[9] Zhang, Y. Ionocovalency and Applications 1. Ionocovalency Model and Orbital Hybrid Scales.Int. J. Mol. Sci. 2010, 11, 4381-4406  

[10] Villesuzanne, A.; Elissalde, C.; Pouchard, M. and Ravez, J. J. Eur. Phy. J. B. 6 (1998) 307.
[11] Ravez, J.; Pouchard, M.; Hagenmuller, P., Eur. J. Solid State Inorg. Chem., 1991,        25, 1107.

[12] Taube, H. a personal letter to Zhang, October 3, 1984.

[13] Pauling, L. a personal letter to Zhang, February 6, 1981.
[14] Zhang, Y. Inorg Chem. 21 (1982) 3889.
[15] Pearson, R. G., J. Am. Chem. Soc. 1963, 85, 3533; J. Chem. Educ.,1968, 45, 581.
[16] Klopman, G. J. Am. Chem. Soc. 1968, 90, 223.
[17] Yingst, A. and McDaniel, D. H. Inorg. Chem.1967, 6, 1076.
[18] Aharland, S. Chem. Phys. Lett., 1968, 2, 303; Struct. Bond., 1, 207.

[19] International Ionocovalency Schools -

 

 

Picture                          Pauling Electronegativity (top) and Zhang Electronegativity (below)

 

 

PictureHundreds of appreciation letters and cards for Zhang Electronegativity published

 

 

PictureLetter from Nobel Laureate Henry Taube

 

 

PictureLetter from Nobel Laureate Linus Pauling

 

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