Atomic bonds History

Ultimately, fracture results from the breaking of atomic bonds. For a brittle solid, the balancing of the energy release rate G and the dissipative processes associated with the creation of new free surface is played out explicitly on an atom by atom basis if one carries out a molecular dynamics simulation of the relevant atomic-level processes. A number of calculations illustrate the level to which such calculations can be pushed using parallel versions of molecular dynamics codes. An especially beautiful sequence of snapshots from the deformation history of a solid undergoing fracture is shown in fig. 12.33. The key point illustrated by... 

After an introductory section with a brief account of the history of intermetallics, the fundamentals of intermetallics are discussed by making reference to the respective chapters in various volumes of MST. In particular, the stability of phases, as well as the relation between atomic bonding and basic properties are addressed, and the criteria for grouping the various phases are discussed. Then the various intermetallics and the respective materials developments are described, and finally the prospects, as well as the needs for research and development, are assessed. 

The expert is aware that the electron s history has no significance, but a learner may well expect there to be a greater attraction between an atomic core and the bonding electron that belongs to that atom (Taber, 1998). Such beliefs may seem rather bizarre for those used to thinking of chemistry in terms of fundamental concepts (such as energy and forces), but actually reflect one of the basic principles of magic that seem to commonly influence people s intuitions about the natural world (Nemeroff Rozin, 2000). Indeed the notion that a past association leaves some... 

The history and development of polysilane chemistry is described. The polysilanes (polysilylenes) are linear polymers based on chains of silicon atoms, which show unique properties resulting from easy delocalization of sigma electrons in the silicon-silicon bonds. Polysilanes may be useful as precursors to silicon carbide ceramics, as photoresists in microelectronics, as photoinitiators for radical reactions, and as photoconductors. 

This chapter is based on the VSEPR and LCP models described in Chapters 4 and 5 and on the analysis of electron density distributions by the AIM theory discussed in Chapters 6 and 7. As we have seen, AIM gives us a method for obtaining the properties of atoms in molecules. Throughout the history of chemistry, as we have discussed in earlier chapters, most attention has been focused on the bonds rather than on the atoms in a molecule. In this chapter we will see how we can relate the properties of bonds, such as length and strength, to the quantities we can obtain from AIM. 

The term molecular crystal refers to crystals consisting of neutral atomic particles. Thus they include the rare gases He, Ne, Ar, Kr, Xe, and Rn. However, most of them consist of molecules with up to about 100 atoms bound internally by covalent bonds. The dipole interactions that bond them is discussed briefly in Chapter 3, and at length in books such as Parsegian (2006). This book also discusses the Lifshitz-Casimir effect which causes macroscopic solids to attract one another weakly as a result of fluctuating atomic dipoles. Since dipole-dipole forces are almost always positive (unlike monopole forces) they add up to create measurable attractions between macroscopic bodies. However, they decrease rapidly as any two molecules are separated. A detailed history of intermolecular forces is given by Rowlinson (2002). 

The landmark in the history of conformation started in 1874 when van t Hoff and Le Bel gave the tetrahedral structure of the carbon atom in which the angle between the valency bonds was... 

Although, in principle, the chemistry here reported should be centered on the late transition metals, sometimes we will jump the frontier between late and middle or early transition metal since this line could be more or less diffuse and could change as a function of the history. At least seven different coordination modes have been identified (I-VII, Scheme 3) as the main bonding modes. In modes I and II the ylide behaves as neutral and monodentate, bonded exclusively through the Ca atom (kC mode) this is the case for simple ylides and carbodipho-sphoranes. Mode 111 covers the variants of a metallated ylide, that is, a situation in which the metal replaces a substituent of the ylide and transforms it into an anionic ligand. 

Snch was once the good fortnne of the atom. There were secret bonds and nnclear wedlock, and behold The whole history of time is thrown open for all to see. Lucretius sings once more and snpemovas burst out laughing in the face of the Universe. 

Dimesityldioxirane, a crystalline derivative, has been isolated by Sander and colleagues and subjected to X-ray analysis. The microwave and X-ray data both suggest that dioxiranes have an atypically long 0—0 bond in excess of 1.5 A. Those factors that determine the stability of dioxiranes are not yet completely understood but what is known today will be addressed in this review. A series of achiral, and more recently chiral oxygen atom transfer reagents, have been adapted to very selective applications in the preparation of complex epoxides and related products of oxidation. A detailed history and survey of the rather remarkable evolution of dioxirane chemistry and their numerous synthetic applications is presented in Chapter 14 of this volume by Adam and Cong-Gui Zhao. Our objective in this part of the review is to first provide a detailed theoretical description of the electronic nature of dioxiranes and then to describe the nuances of the mechanism of oxygen atom transfer to a variety of nucleophilic substrates. 

Only after the atomic weight units of composition were established, was it possible for chemists to arrange those units successfully in meaningful molecular arrays and conceive the ideas of valence and directional bonding. Molecular structure remains today the central theoretical focus of attention, whether in the realm of molecular biology, biochemistry, chemical pharmaceutics, or polymer plastics. Daltons atomic theory must be seen as the climax of the history of chemical composition and terminates this story. ... 

The interiors of planets, moons, and many asteroids either are, or have been in the past, molten. The behavior of molten silicates and metal is important in understanding how a planet or moon evolved from an undifferentiated collection of presolar materials into the differentiated object we see today. Basaltic volcanism is ubiquitous on the terrestrial planets and many asteroids. A knowledge of atomic structure and chemical bonding is necessary to understand how basaltic melts are generated and how they crystallize. Melting and crystallization are also important processes in the formation of chondrules, tiny millimeter-sized spherical obj ects that give chondritic meteorites their name. The melting, crystallization, and sublimation of ices are dominant processes in the histories of the moons of the outer planets, comets, asteroids, and probably of the Earth. 

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