Sanderson electronegativity

In 1951, Robert Thomas Sanderson (1912-1989) introduced the principle of electronegativity equalization that proposes, when two or more atoms combine, the atoms adjust to the same intermediate Mulliken electronegativity (Sanderson, 1951). Density functional theory tells us that the Mulliken electronegativity is the negative of the chemical potential (Parr et al., 1978). Sanderson s principle then becomes very appealing in that it can be considered analogous to a macroscopic thermodynamic phenomenon - the equalization of chemical potential. When atoms interact, the electronegativity, or chemical potential, must equalize. 

Oxidation state Ionic radii (A) Electronegativity (Pauling) Electronegativity (Sanderson)... 

Sanderson calls his electronegativity stability ratio SR. The electronegativity in this scale is x(SR) = n/(4.19 r ), in which n is the number of valence electrons and r the covalent atomic radius. It also expresses the influence that atomic volume has on electronegativity. Sanderson was the first to point out the electronegativity equalization principle. Although the -values are different in the various scales as is clear from Table 2.4, all the electronegativity scales correlate strongly with one another. 

The relative electronegativity X-weighting scheme (Balaban, 1986 Balaban and Ivanciuc, 1989) Sanderson electronegativities (Sanderson, 1983). 

TABLE 1.1 Electronegativities of Some Atoms on the Pauling" and Sanderson Scales... 

Figure 2. (A) v(OH) ( ) and the v(=CH) ( ) wavenumbers of MBOH adsorbed on zeolites as a function of Sanderson electronegativity (B) Intensity of v(OH) band created by dissociated H2S as a function of Sanderson electronegativity...

Table 4.7. Natural electronegativity values Xm(N) ( Pauling units ) for d-block (group 3-11) elements of the first three transition series (Sanderson values19 xfs> for the first transition series are given in parentheses)...

These descriptors have been widely used for the past 25 years to study chemical reactivity, i.e., the propensity of atoms, molecules, surfaces to interact with one or more reaction partners with formation or rupture of one or more covalent bonds. Kinetic and/or thermodynamic aspects, depending on the (not always obvious and even not univoque) choice of the descriptors were hereby considered. In these studies, the reactivity descriptors were used as such or within the context of some principles of which Sanderson s electronegativity equalization principle [16], Pearson s hard and soft acids and bases (HSAB) principle [17], and the maximum hardness principle [17,18] are the three best known and popular examples. 

One of the parameters in the broad class of liquid adsorption mechanisms is the interaction between the acidic and basic sites of the adsorbent and the adsorbate. The acidity of zeolitic adsorbent is normally affected by the zeolite Si02/Al203 molar ratio, the ionic radii and the valence of the cations exchanged into the zeolite. In this contribution, Sanderson s model of intermediate electronegativity of zeolitic adsorbent acidity (SjJ can be calculated as a representation of the strength of the adsorbent acidity based on the following equation ... 

According to Sanderson (1960), electronegativity represents the mean electron density per unit volume of an inert element ... 

Electronegativity values according to Pauling and Sanderson are listed in table 1.6, together with the first four ionization potentials and the electron affinities of the various elements. 

Table 1.6 Elemental properties first four ionization potentials (II, 12,13,14, from Samsonov, 1968 values expressed in eV values in parentheses are of doubtful reliability) electron affinity (e.a., from Samsonov, 1968 eV) Pauling s electronegativity (P, from Samsonov, 1968 eV) Sanderson s electronegativity (S, from Viellard, 1982 adimensional). 

The crudest one is Sanderson s electronegativity equalization principle [39, 40] according to which atoms-in-molecule make electron transfers from lower to higher electronegative parts thus achieving equilibrium in electronegativity. 

Another definition that is based on size and charge, hut in a unique way, is the definition of Sanderson,47 which is based on relative electron density. This method has never been accepted widely, although Sanderson has applied it successfully to a variety of problems,48 and his values were the first to illustrate the interesting electronegativity properties of the posUransttton elements (see Chapter 16). 

Microcrystalline solids such as zeolites and zeolite like structures have shown the utility of those properties in the domain of acid catalysis. However, little is known on their possibilities as base catalysts. It has been shown [ref. 1,2] that zeolites have basic sites which are able to catalyze reactions needing weak and medium basic strengths. Moreover, a correlation between the basicity and the Sanderson s average electronegativity Df the framework has been observed [ref. 3], Then, their activity as base catalysts can be modified by changing the countercation [ref. 4], the framework Si/Al ratio, or by introducing atoms other than Si and Al in the framework [ref. 5],... 

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