Bonding theories of metals

Linus Pauling, A Resonating-Valence-Bond Theory of Metals and Intermetallic Com-... 

A resonating-valence-bond theory of metals and intermetallic compounds... 

The resonating-valence-bond theory of metals discussed in this paper differs from the older theory in making use of all nine stable outer orbitals of the transition metals, for occupancy by unshared electrons and for use in bond formation the number of valency electrons is consequently considered to be much larger for these metals than has been hitherto accepted. The metallic orbital, an extra orbital necessary for unsynchronized resonance of valence bonds, is considered to be the characteristic structural feature of a metal. It has been found possible to develop a system of metallic radii that permits a detailed discussion to be given of the observed interatomic distances of a metal in terms of its electronic structure. Some peculiar metallic structures can be understood by use of the postulate that the most simple fractional bond orders correspond to the most stable modes of resonance of bonds. The existence of Brillouin zones is compatible with the resonating-valence-bond theory, and the new metallic valencies for metals and alloys with filled-zone properties can be correlated with the electron numbers for important Brillouin polyhedra. 

The distances found between platinum centers in these molecules have been correlated with the resonating valence bond theory of metals introduced by Pauling. The experimentally characterized partially oxidized one-dimensional platinum complexes fit a correlation of bond number vs. metal-metal distances, and evidence is presented that Pt—Pt bond formation in the one-dimensional chains is resonance stabilized to produce equivalent Pt—Pt distances.297 The band structure of the Pt(CN)2- chain has also been studied by the extended Huckel method. From the band structure and the density of states it is possible to derive an expression for the total energy per unit cell as a function of partial oxidation of the polymer. The equilibrium Pt-Pt separation estimated from this calculation decreases to less than 3 A for a loss of 0.3 electrons per platinum.298... 

This view is really an oversimplification that fails to explain metals in a quantitative way, nor can it account for the differences in the properties of individual metals. A more detailed treatment, known as the bond theory of metals, applies the idea of resonance hybrids to metallic lattices. In the case of an alkali metal, for example, this would involve a large number of hybrid structures in which a given Na atom shares its electron with its various neighbors. 

A review of the unsynchronized-resonating-covalent-bond theory of metals in presented. Key concepts, such as unsynchronous resonance, hypoelectronic elements, buffer elements, and hyperelectronic elements, are discussed in detail. Application of the theory is discussed for such things as the atomic volume of the constituents in alloys, the structure of boron, and superconductivity. These ideas represent Linus Pauling s understanding of the nature of the chemical bond in metals, alloys, and intermetallic compounds. 

One of the salient features of the unsynchronized-resonating-covalent-bond-theory of metals, alloys, and intermetallic compounds is that, on average, 0.72 of an orbital per... 

One of the lasting practical results of treating metals in this model has been the tabulation of atomic radii and interatomic distances in metals [39-42]. Another interesting application of the unsynchronized-resonating-covalent-bond-theory of metal is its use in the elucidation of the to the structure and properties of elemental boron and the boranes [43]. 

In a footnote to his 1949 paper entitled A Resonating-Valence-Bond Theory of Metals and Intermetallic Compounds, Linus Pauling gave an example of a simple statistical treatment to derive the metallic orbital [27]. Nevertheless, it took him three and one-half decades to publish the detailed statistical treatment [34-36], which is given in the following. 

SUPERCONDUCTIVITY INTERPRETED IN TERMS OF THE UNSYNCHRONIZED-RESO-NATING-COVALENT-BOND THEORY OF METALS... 

Another interesting application of the unsynchronized-resonating-covalent-bond theory of metals to superconductivity is the elucidation of the mechanism of superconductivity in the substances K3C60 and RbaCgO) for which superconducting transition temperatures of 19.3 K [122] and 28 K [123], respectively, have been found [124], The crystal structure of K3C60 was reported in 1991 [125]. The salient features of the structure are shown in Figure 12. 

L. Pauling, A resonating-valence-bond theory of metals and intermetallic compounds. Proc. Roy. Soc. (London) A196, 343-362 (1949). 

L. Pauling and Z. S. Herman, Recent advances in the unsynchronized-resonating-covalent-bond theory of metals, alloys, and intermetallic compounds and its application to the investigation of the structure of such systems, in Modelling of Structure and Properties of Molecules, Z. B. Maksic, ed., Ellis Horwood, Chichester, England, 1987, pp. 5-37. 

The valence-bond theory of metals is of importance in that it enables us to form a qualitative picture of the properties of these elements. In the first place it explains the close relationship, already mentioned in 5.07, between metallic and covalent radii, since it treats metallic binding as being essentially covalent in origin. A second important feature is that it enables us to understand the distribution of the metallic elements in the Periodic Table, as we may now show. 

The Pauhng resonating-bond theory of metals opened up a radically new line of approach to the study of the bonding of adsorbed gases and the im-... 

Besides the electron occupation of the d bands, another description can be used for obtaining correlations, namely, the valence bond theory of metals. The bonding in a transition metal is partially due to impaired electrons in bonding d orbitals. The contribution of these d electrons to the valence bonding was termed percentage d... 

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