Absolute electronegativity, definition

Both of the xp and Xm scales are empirical approximations based on incomplete experimental data. The theoretical definition of absolute electronegativity, x = a/Eg = /Xm — > Xv has been demonstrated to account for both empirical scales. The scale factor x varies with periodic shell and //, represents the number of valence energy-level vacancies. 

This definition of hardness is related to Mulliken s definition of electronegativity, called absolute electronegativity by Pearson ... 

Related procedures for estimating electron affinities make use of the concept of electronegativity (EN). These use the Mulliken [33] definition of absolute electronegativity, the average of the first ionization potential and the first electron affinity, EN = (IP + EA)/2. With an estimate of the Mulliken electronegativity and the experimental value of the ionization potential, the electron affinities can be calculated. When both the electron affinity and ionization potential are measured, the relationship between the EN and experiment can be examined. This has been accomplished for aromatic hydrocarbons and will be discussed in Chapter 10. 

Hard and soft acid and base theory gives access to an early part of the slope in a reaction profile like that in Fig. 3.3, just as perturbation molecular orbital theory does. Using the definitions of absolute electronegativity and absolute hardness derived in Equations 3.5 and 3.6, the (fractional) number of electrons AN transferred is given by Equation 3.14. 

Being the actual numerical model mainly a rationalization of the experimental facts, let s involve other estimable quantities. The IP, closely related also with the actual absolute electronegativity (4.253) definition, is a quite accessible spectral atomic index, either theoretical from the limit frequency from which the continuum spectmm is achieved, or experimentally by a Franck-Hertz experiment. Nevertheless, as far as all the valence... 

Because this definition is not dependent on an arbitrary relative seale, it has also been termed absolute electronegativity, with the units of kilojoules per mole or electron volts. If an element has low values of both El and EA, as is the ease of most metals, electronegativity is also low. 

According to the definition in equation (A.2), the absolute electronegativity of an atom is a function of its chtirge ... 

As noted before in the literature the Lapladan V bcp of 1 electron density pbcp at the BCP is correlated to pbcp (and hence to the BV), but obviously also to the degree of bond imiicity (which can e.g. be expressed by the electronegativity or hardness differences of catimi and anion). Using absolute electronegativity differences Xdiff (in eV) based on Mulliken s electronegativity definition [19]... 

Usually, the hardness is seen only as a companion to electronegativity, i.e., associated with the second order effects, as its Parr-Pearson basic (3.3) and (4.251) definitions reflect. This is also the case when the absolute actual picture is employed, a statement supported also by the close quantitative atomic rff and r p scales as the representations from the Figure 4.13 indicate. Instead, when the absolute approach is performed the situation regarding both qualitative and quantitative absolute hardness scale completely changes. Actually, the //J/ values predict a smooth increase of the hardness effects paralleling those of compare the Figures 4.13 and 4.12, respectively. Remarkably, the linked behavior of with is achieved even their basic definitions, Eqs. (4.254) and (4.256), respectively, are not directly related, as there are, for instance, the definitions of... 

The absolute hardness is not to be confused with the Mulliken-Jaffe definition of electronegativity, given by Equation (14.25), where the electronegativity / is defined as the average of the IE and EA (for the valence electrons). The absolute hardness and... 

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