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Chemical bonding electrical effect

Both of the above approaches rely in most cases on classical ideas that picture the atoms and molecules in the system interacting via ordinary electrical and steric forces. These interactions between the species are expressed in terms of force fields, i.e., sets of mathematical equations that describe the attractions and repulsions between the atomic charges, the forces needed to stretch or compress the chemical bonds, repulsions between the atoms due to then-excluded volumes, etc. A variety of different force fields have been developed by different workers to represent the forces present in chemical systems, and although these differ in their details, they generally tend to include the same aspects of the molecular interactions. Some are directed more specifically at the forces important for, say, protein structure, while others focus more on features important in liquids. With time more and more sophisticated force fields are continually being introduced to include additional aspects of the interatomic interactions, e.g., polarizations of the atomic charge clouds and more subtle effects associated with quantum chemical effects. Naturally, inclusion of these additional features requires greater computational effort, so that a compromise between sophistication and practicality is required. [Pg.6]

Methods have been presented, with examples, for obtaining quantitative structure-property relationships for alternating conjugated and cross-conjugated dienes and polyenes, and for adjacent dienes and polyenes. The examples include chemical reactivities, chemical properties and physical properties. A method of estimating electrical effect substituent constants for dienyl and polyenyl substituents has been described. The nature of these substituents has been discussed, but unfortunately the discussion is very largely based on estimated values. A full understanding of structural effects on dienyl and polyenyl systems awaits much further experimental study. It would be particularly useful to have more chemical reactivity studies on their substituent effects, and it would be especially helpful if chemical reactivity studies on the transmission of electrical effects in adjacent multiply doubly bonded systems were available. Only further experimental work will show how valid our estimates and predictions are. [Pg.727]

Quantum Systems in Chemistry and Physics is a broad area of science in which scientists of different extractions and aims jointly place special emphasis on quantum theory. Several topics were presented in the sessions of the symposia, namely 1 Density matrices and density functionals 2 Electron correlation effects (many-body methods and configuration interactions) 3 Relativistic formulations 4 Valence theory (chemical bonds and bond breaking) 5 Nuclear motion (vibronic effects and flexible molecules) 6 Response theory (properties and spectra atoms and molecules in strong electric and magnetic fields) 7 Condensed matter (crystals, clusters, surfaces and interfaces) 8 Reactive collisions and chemical reactions, and 9 Computational chemistry and physics. [Pg.434]

Table 7-1 lists four types of electrical attractions that can occur between these particles. The strength of even the strongest of these attractions is many times weaker than any chemical bond, however. The attraction between two adjacent water molecules, for example, is about 20 times weaker than the covalent bonds holding the hydrogen and oxygen atoms together in the water molecules. Although particle-to-particle attractions are relatively weak, you can see their profound effect on the substances around you. [Pg.222]

In addition to the orbitals shown in Fig. 1 there are hybrid orbitals that are not stationary states for the electron in an isolated atom. They can be obtained by taking a linear combination of the standard orbitals in Fig. 1. Since the electron distribution is off center they are useful only for atoms that are perturbed by an electric field (Stark-effect) or by the approach of other atoms as occurs in chemical-bond formation. [Pg.1164]

Chemical bond breaking. The energy required to break the water molecule into hydrogen and oxygen decreases with increasing temperature. The hotter the steam, the less electricity that is required. However, this is a much smaller effect. [Pg.158]

We have seen that electron-transfer reactions can occur at one charged plate. What happens if one takes into account the second plate There, the electron transfer is from the solution to the plate or electronic conductor. Thus, if we consider the two electronic conductor-ionic conductor interfaces (namely, the whole cell), there is no net electron transfer. The electron outflow from one electronic conductor equals the inflow to the other that is, a purely chemical reaction (one not involving net electron ttansfer) can be carried out in an electrochemical cell. Such net reactions in an electrochemical cell turn out to be formally identical to the familiar thermally induced reactions of ordinary chemistry in which molecules collide with each other and form new species with new bonds. There are, however, fundamental differences between the ordinary chemical way of effecting a reaction and the less familiar electrical or electrochemical way, in which the reactants collide not with each other but with separated charge-transfer catalysts, as the two plates which serve as electron-exchange areas might well be called. One of the differences, of course, pertains to the facility with which the rate of a reaction in an electrochemical cell can be controlled all one has to do is electroiucally to control the power source. This ease of control arises because the electrochemical reaction rate is the rate at which the power source pushes out and receives back electrons after their journey around the circuit that includes (Figs. 1.4 and 1.5) the electrochemical cell. [Pg.10]


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See also in sourсe #XX -- [ Pg.110 , Pg.111 , Pg.128 ]




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