Valence (chemistry)

About: Valence (chemistry) is a research topic. Over the lifetime, 24937 publications have been published within this topic receiving 645252 citations. The topic is also known as: valency.

Electronic Band Structure of {Al2O3}, with Comparison to Alon and {AIN}

Abstract: As the uses of Al2O3 and other ceramics expand into new and more demanding applications, it is increasingly important to understand their electronic structure and its relationship to properties. However, compared with metals, semiconductors, or alkali halides, our understanding of the electronic structure of ceramic materials is limited. There has been much recent progress in our understanding of the electronic structure of Al2O3, based on the applications of new experimental and theoretial methods. Vacuum ultraviolet spectroscopy and valence band photoemission spectroscopy coupled with pseudofunction band structure methods provide a comprehensive approach to study a wide variety of electronic structure issues of importance to ceramic materials. The high-temperature electronic structure and its role in determining the high-temperature, intrinsic, electronic conductivity gives us the ability to evaluate high-temperature conductivity data, and supports the conclusion that Al2O3 is predominantly an electronic conductor at high-temperatures. The strain dependence of the electronic structure, as embodied in the deformation potentials, provides a simple method to determine surface stresses and strains. The variation of the electronic structure in the family Al2O3-AION-AIN demonstrates the changes associated with the valence band chemistry of changing the anion from oxygen to nitrogen, and the bonding from mixed ioniccovalent in the direction of greater covalency. These changes in the anion valence bands lead to dramatic changes in the atomic and electronic nature of room-temperature bimaterial interface formation for copper to Al2O3 or AIN. The application of this new methodology to develop our perspective on electronic structure and apply it to problems associated with temperature, stress, composition, or interface formation can improve our understanding of many critical questions in ceramics.

Intervalence Charge Transfer and Electron Exchange Studies of Dinuclear Ruthenium Complexes

Abstract: Publisher Summary This chapter discusses the theory of mixed-valence systems and theory of electron exchange. In the case of strong coupling, for which it is no longer appropriate to use perturbation theory, the interaction of states is so great that bonding and antibonding potential energy curves result. Because the ground state is delocalized between metal ions, it is not strictly appropriate to describe the intervalence transition band of a class III complex as a metal-to-metal charge transfer transition. The metal-to-metal charge transfer (MMCT) designation is used for the sake of simplicity. The dependence of intervalence transition energy on the activation barrier to thermal electron transfer allows the solvent dependence of intervalence transitions to be understood in terms of relationships developed for the Marcus Theory of electron transfer. The Hush model is the preferred method of analysis of mixed valence complexes for the experimentalist because of its readily understandable derivation, its overlap with the Marcus theory of electron transfer, and the facility of its application. However, it is applicable only to weakly coupled class II complexes. A quantitative theory that is applicable to all mixed valence complexes is desirable.