Many-electron atom electronic structure

The observed structure of the spectra of many-electron atoms is entirely accounted for by the following postulate Only eigenfunctions which are antisymmetric in the electrons , that is, change sign when any two electrons are interchanged, correspond to existant states of the system. This is the quantum mechanics statement (26) of the Pauli exclusion principle (43). 

In recent years the old quantum theory, associated principally with the names of Bohr and Sommerfeld, encountered a large number of difficulties, all of which vanished before the new quantum mechanics of Heisenberg. Because of its abstruse and difficultly interpretable mathematical foundation, Heisenberg s quantum mechanics cannot be easily applied to the relatively complicated problems of the structures and properties of many-electron atoms and of molecules in particular is this true for chemical problems, which usually do not permit simple dynamical formulation in terms of nuclei and electrons, but instead require to be treated with the aid of atomic and molecular models. Accordingly, it is especially gratifying that Schrodinger s interpretation of his wave mechanics3 provides a simple and satisfactory atomic model, more closely related to the chemist s atom than to that of the old quantum theory. 

The polysilanes are compounds containing chains, rings, or three-dimensional structures of silicon atoms joined by covalent bonds. Recently, polysilane high polymers have become the subject of intense research in numerous laboratories. These polymers show many unusual properties, reflecting the easy delocalization of sigma electrons in the silicon-silicon bonds. In fact, the polysilanes exhibit behavior unlike that for any other known class of materials. 

In Chap. 3 the elementary structure of the atom was introduced. The facts that protons, neutrons, and electrons are present in the atom and that electrons are arranged in shells allowed us to explain isotopes (Chap. 3), the octet rule for main group elements (Chap. 5), ionic and covalent bonding (Chap. 5), and much more. However, we still have not been able to deduce why the transition metal groups and inner transition metal groups arise, why many of the transition metals have ions of different charges, how the shapes of molecules are determined, and much more. In this chapter we introduce a more detailed description of the electronic structure of the atom which begins to answer some of these more difficult questions. 

The electronic structure of the atoms. The electronic structure of the atoms of the different elements and their relation to the characteristics of the Periodic Table are based on a number of experimental data and theoretical models which are fully discussed in many elementary and advanced texts of inorganic chemistry such as Cotton et al. (1999), Greenwood and Earnshaw (1997), Huheey etal. (1997), Wells (1984). 

Rutherford s discovery of the atomic nucleus was his greatest contribution to physics and it established him as the leading experimental physicist of his day. However, it was only a beginning, and many questions about the atom remained unanswered. As yet nothing was known about electron orbits or about the relationship between the structure of the atom and the periodic table. Before Rutherford performed his experiments, it was thought that the atom was understood. Now it was apparent that much remained to be learned. But then great discoveries in physics seem always to suggest new questions and open up new lines of research. The more that is known, the better the picture scientists have of what remains unknown. 

The many-body perturbation theory [39] [40] [41] was used to model the electronic structure of the atomic systems studied in this work. The theory developed with respect to a Hartree-Fock reference function constructed from canonical orbitals is employed. This formulation is numerically equivalent to the M ler-Plesset theory[42] [43]. 

Nonstoichiometric compounds are mixed-valence compounds with nonintegral electron/atom ratios. Electronic properties of these compounds depend crucially on the nature and magnitude of nonstoichiometry. Electronic conduction in many such compounds occurs by hopping between the cations of different valencies (e.g. Pr " " and Pr" " in Pri2022)- Nonstoichiometry with a wide range of compositions is more common in oxides, sulphides, and related materials where the bonding is not completely ionic. In ionic nonstoichiometric compounds, structural rearrangements... 

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