Pauling models

Figure 9. Scheme of oxygen adsorption models (a) die Griffiths model, (b) die Pauling model, and (c) the Yeager model. 

R. Ahlrichs, Gillespie- und Pauling-Modell - ein Vergleich, Chem. unserer Zeit, 1980, 14, 18-24. 

Amyes, T. L. Richard, J. P. Specificity in transition state binding The Pauling model revisited, Biochemistry 2013, 52, 2021-2035. 

The Knudsen effusion method In conjunction with mass spectrometrlc analysis has been used to determine the bond energies and appearance potentials of diatomic metals and small metallic clusters. The experimental bond energies are reported and Interpreted In terms of various empirical models of bonding, such as the Pauling model of a polar single bond, the empirical valence bond model for certain multiply-bonded dlatomlcs, the atomic cell model, and bond additivity concepts. The stability of positive Ions of metal molecules Is also discussed. 

The use of empirical models of bonding has been Invaluable for the interpretation of the experimental dissociation energies of diatomrLc Intermetallic molecules as well as for the prediction of the bond energies of new molecules. In the course of our work, conducted for over a decade, we have extended the applicability of the Pauling model of a polar single bond (31) and have developed new models such as the empirical valence bond model for certain multiple bonded transition metal molecules (32,33) and the atomic cell model (34). 

According to the Pauling models the bond energy, D(A-B) of a diatomic molecule, AB, may be expressed by the relation ... 

A comparison of experimental values for intermetallic diatomic molecules with gold with the corresponding value calculated by the Pauling model and by the atomic cell model has been given in Table 6 of Reference ( ). Table 7 of Reference ( ) shows a comparison between experimental dissociation energies with values calculated by the atomic cell model and the empirical valence bond model. Table 9 of Reference ( ) takes Mledema s refinements (43) of the atomic cell model into account In these comparisons. 

There are important differences between the literature models and our results. In our case, (i) the number of monomers is smaller than that in the Pauling model (where they are present in clathrate-like cages), and (ii) they coexist with a disturbed but still infinite, not disintegrated network of water molecules. In contrast, the models in refs 11 and 32 do not involve a network but only a distribution of clusters. 

Empirical models have been developed to predict the bond energies of metallic and intermetallic molecules, such as the following the Pauling model of a polar single bond [174], the valence bond model for certain multiply bonded metallic molecules by Brewer [175] and Gingerich [176], and the macroscopic atom or atomic cell model by Miedema and Gingerich [177]. 

The reason that all the arguments of the previous section are consistently ignored by chemists lies with the number of undergraduate textbooks that repeat the Pauling model as scientific fact. After fifty years, a tradition, established over generations of chemists, is no longer subject to scrutiny. It may therefore help to re-examine some of the original assumptions. 

Mainly because of a dimensional misfit between the T and O sheets (cf below), in real mica structures the Pauling model (in which there are no structural distortions) is too abstract and must be replaced at least by a model which takes into account a rotation of the tetrahedra within the (001) plane. This ditrigonal rotation is discussed below the resulting model has been called the trigonal model by Nespolo et al. (1999c). 

As already mentioned, in real mica structures the Pauling model is too abstract and must be replaced at least by the trigonal model, which considers a rotation of the tetrahedra around the perpendicular to (001). In fact, h being about 9.4, 8.6 and 9.3 Ain brucite, gibbsite and T sheet (with Si Al = 3 1), respectively, the dimensions of the T and of the O sheets do not match. Consequently, as discussed below, some structural distortions are needed to overcome the misfit and to form these two sheets into a layer. 

S ow. These are the rows with h = 0(mod3) and k =0(mod3) they are family rows in the Pauling model and are common to all polytypes of the same family. 

X-pp ellipes. The intensity distribution in the 1st ellipse (as well as other X-type ellipses) is typical of each mica polytype. Knowing the symmetry principle (subfamily A or B, or mixed-rotation, revealed by the 2nd ellipse) helps to obtain the stacking sequence from the intensity distribution in the 1st ellipse. Because the X rows are non-family rows in both the Pauling and trigonal model, the computation of the intensities in the X-type ellipses, to be compared with those experimentally measured, can be performed even in the simplest Pauling model. 

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