Chemical bonding atomic-number dependence

Theoretical studies on the atomic number dependence of the relative effects on chemical bonding, including polonium, have been carried out, " for example PoFg was investigated. An analysis of bond overlap population using both nonrelativistic and relativistic DV-Xa molecular orbital calculations was... 

Atomic-number dependence of relativistic effects on chemical bonding... 

The Atomic-number dependence of the relativistic effects on chemical bonding has been studied using the difference (APb) in the bond overlap populations between the relativistic and nonrelativistic DV-Xa calculations for various XH diatomic hydrides (X=Cu, Ag, and Au) and XFe hexafluorides (X=S, Se, Mo, Ru, Rh, Te, W, Re, Os, Ir, Pt, U, Np, and Pu). The atomic-number dependence of APb suggests that the absolute values of APb roughly increase with order (aZ)2 for Z up to about 80, and the higher order term (aZ) should be... 

KEYWORDS Relativistic effects bond overlap population atomic-number dependence chemical bonding DV-Xa... 

DV-Xa methods. It was found that relativistic effects become significant in chemical bonding of molecules containing heavy elements with Z larger than 50 and APb of the XFg (X=S to W) shows a Z -dependence similar to that of ARg for the hydrides [1]. On the other hand, the atomic-number dependence of APb for actinide compounds such as UFg was not well explained using the Z -dependence. However, the number of examples examined in the previous work are not satisfactory for discussing the reason for the dependence of APb-... 

The aim of the present work is to obtain the general trend of the atomic-number dependence of the relativistic effects on chemical bonding by examining... 

Atomic-Number Dependence of Relativistic Effects on Chemical Bonding... 

In order to explain the atomic-number dependence of the relativistic effects on chemical bonding, the absolute value of APb, IAPbI, was introduced. Figure 2 shows the plot of IAPbI as a function of Z , along with the results of the six times value of IAPbI for CuH, AgH, and AuH diatomic hydrides. The reason for the... 

Onoe, J. Atomic-number dependence of relativistic effects on chemical bonding. Adv. Quant. Chem. 37, 311-323 (2000)... 

We now know that electrons in atoms can hold only particular energies and that their probable whereabouts are described by Schrodiiiger s wave function. The energies and probable locations depend on integer numbers, or quantum numbers. Quantum numbers describe the energy and geometry of the possible electronic states of an atom. These states, in turn, deteriiiilie the chemical behavior of the elements—that is, how chemical bonds can form. 

The variation of the Chin-Gilman parameter with bonding type means that the mechanism underlying hardness numbers varies. As a result, this author has found that it is necessary to consider the work done by an applied shear stress during the shearing of a bond. This depends on the crystal structure, the direction of shear, and the chemical bond type. At constant crystal structure, it depends on the atomic (molecular volume). In the case of glasses, it depends on the average size of the disorder mesh. 

We underline these results and the implied concepts quoting from a comprehensive review on this subject (Simon 1983). We remember indeed that, ever since it was experimentally possible to determine atomic distances in molecules and crystals, efforts have been made to draw conclusions about the nature of the chemical bonding, and to compare interatomic distances (dimensions) in the compounds with those in the chemical elements. Distances between atoms in an element can be measured with high precision. As such, however, they cannot be simply used in predicting interatomic distances in the compounds. In a rational procedure, reference values (atomic radii) have to be extracted from the individual (interatomic distances) measured values. Various functions have been suggested for this purpose. In the specific case of the metals it has been pointed out that interatomic distances depend primarily on the number of ligands and on the number of valence electrons of the atoms (Pearson 1972). 

To use Equation 2 to determine s electron density diflFerences, it must be "calibrated —i.e., source-absorber or absorber-absorber combinations must be found for which the 5 electron density diflFerence is known. The most common method for calibrating the isomeric shift formula is to measure isomeric shifts for absorbers with diflFerent numbers of outer shell 5 electrons—e.g., by using compounds with the absorbing atoms in different valence states. The accuracy of this method depends on how much is known about the chemical bonds in suitably chosen absorber compounds, in particular about their ionicity and their hybridization. t/ (0) 2 can be obtained for an outer 5 electron from the Fermi-Segre formula or preferably from Hartree-Fock calculations. 

The periodic system developed from Bohr s atomic theory is of the greatest importance in chemical science because it demonstrates that the properties of the elements depend on their positions in the system. It is immediately apparent that chemical valency depends on the number of loosely-bound electrons in the atom. Thus, the alkali metals have one such electron while the divalent alkaline-earth metals have two, etc. Valency is therefore closely connected with electronic structure and provides the foundation for the modern theory of the chemical bond, the basis of which is to be found in the coupling or transfer of the valency electrons. 

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