Electric charge distribution

The and Oj terms always contribute, regardless of the specific electric charge distributions ia the adsorbate molecules, which is why they are called nonspecific. The third nonspecific Op term also always contributes, whether or not the adsorbate molecules have permanent dipoles or quadmpoles however, for adsorbent surfaces which are relatively nonpolar, the polarization energy Op is small. 

The Self-Consistent Reaction Field (SCRF) model considers the solvent as a uniform polarizable medium with a dielectric constant of s, with the solute M placed in a suitable shaped hole in the medium. Creation of a cavity in the medium costs energy, i.e. this is a destabilization, while dispersion interactions between the solvent and solute add a stabilization (this is roughly the van der Waals energy between solvent and solute). The electric charge distribution of M will furthermore polarize the medium (induce charge moments), which in turn acts back on the molecule, thereby producing an electrostatic stabilization. The solvation (free) energy may thus be written as... 

Most of biological reactions take place in a highly polarizable medium which contains mobile polar water molecules, reorientable polar groups, and mobile ions. For macroscopic media, the energetics of an electric charge distribution placed in a vicinity of a polarizable medium can be described by means of the classical dielectric theory159. 

The first term in Eq. 4.26 represents Van der Waals forces between atoms of the microscopic environment and the embedded molecule, this term is not involved in the construction of the Fock matrix. The second one represents Coulomb interactions between the embedded electron density and the electric charge distribution in the environment which is approximated by point charges. 

Holmes, J. C., J. E. Hardcastle and R. I. Mitchell, The determination of particle size and electric charge distribution in cigarette smoke, Tobacco Science, 3 148-153 (1959). 

Neutral molecules can be represented as systems of electric charges distributed in space. Positive charge is concentrated in the atomic nuclei, and negative... 

In exposures of humans to artificially generated aerosols, where the information is to be relevant to ambient aerosols, several factors are important the particle diameter distribution must be fairly constant and fall within size ranges typical for the given compound in the ambient air, the chemical composition of the aerosol must be stable and predictable, and the electric charge distribution of the aerosol must simulate that of normal atmospheric aerosols. 

I. 46. The magnitude of the coefficient reflects the electric charge distribution of the ionic species. A 0.1 molal solution of Al2(S04)3 has an activity coefficient of only 0.035. It should also be noted that, in dilute solutions, activity coefficients of electrolytes decrease in magnitude with increasing concentration. A minimum is reached and the coefficient then increases with concentration. See Activity Debye-Huckel Law Biomineralization... 

Charged Colloids (Electrical Charge Distribution at Interfaces)... 

The acidity of phenols is mainly due to an electrical charge distribution in phenols that causes the —OH oxygen to be more positive. As a result, the... 

There are two nonequivalent pairs of S-F bonds in the sulfur tetrafluoride molecule, the shorter equatorial S-F bonds (1.545 A) and the longer axial S-F bonds (1.646 A). The bond angles arc equally 101 33 and 186" 56 for equatorial and axial bonds, respectively.5 The shorter and the longer S-F bond energies are, respectively, —20.31 and — 13.74 eV. The electric charge distribution in the sulfur tetrafluoride molecule is as follows + 1.70 on the sulfur atom, — 0.35 on the equatorial fluorine atoms and —0.50 on the axial fluorine atoms.5... 

Let us add a few comments on boundaries between phases in nonmetals. Since the boundary in a nonmetallic heterogeneous system is chemically unsymmetric, its electric charge distribution is dipolar, in contrast to a (symmetric) grain boundary. A force can therefore be exerted on this interface by an externally applied electric field. 

Figure 10-6. Various thermodynamic potentials and the electric charge distribution at and near an equilibrium interface (schematic).

Proteins and antibodies are natural substrates for affinity columns because of the nature of the enzyme recognition site and the antibody-antigen interaction sites. They have a three-dimensional shape and electrical charge distributions that interact with only specific molecules or types of molecules. Once these substrate sites are identified, molecules can be isolated or synthesized with the key characteristics and used to build affinity supports. These substrates are often bound to a 6-carbon spacer so that they protrude farther away from the packing surface toward the mobile phase and are therefore more available. Certain natural and synthetic dyes have been found to serve as substrate mimics for a class of enzymes call hydrogenases and have been used to build affinity columns for their purification. 

A polar molecule such as HC1 possesses a permanent dipole moment // by virtue of the non-uniform electric charge distribution within the neutral molecule. The electrostatic energy between two interacting dipoles //1 and 112 is strongly dependent on their relative orientation. If all relative orientations are equally probable and each orientation carries the Boltzmann weighting factor e-cW r, the following expression is obtained ... 

There are interactions between neutral molecules with zero or small permanent dipole moments, referred to as induced dipole-induced dipole interactions. Even though a molecule has no or a small dipole moment, the electric charge distribution... 

The Coulomb force is mediated by (virtual) photons. Following Faraday, we introduce the artificial concept of the electric field E due to an electric charge distribution p(r) ... 

Molecular polarisability is the result of two mechanisms (a) distortional polarisation and (b) orientation polarisation. Distortional polarisation is the result of the change of electric charge distribution in a molecule due to an applied electric field, thereby inducing an electric dipole. This distortional polarisation is coined ad. Permanent dipoles are also present in the absence of an electric field. At the application of an electric field they will orient more or less in the direction of the electric field, resulting in orientation polarisation. However, the permanent dipoles will not completely align with the electric field due to thermal agitation. It appears that the contribution of molecular polarisability from rotation is approximately equal to p2/(3kT). Accordingly, the total molecular polarisability is... 

These macromolecular compounds when dissolved in a suitable polar solvent (generally water) instantly acquire or can be made to acquire large number of elementary electrical charges distributed along the macromolecular chain. In the former case and when the charge that appears spontaneously has its maximum value, these macromolecules are termed low molar-mass (LMM) electrolytes and in other cases weak polyelectrolytes. 

Dispersional Interaction between Molecules. We still wish to consider briefly energies due to interaction between fluctuating induced electric charge distributions of atoms and molecules. In constrast to electrostatic and induced interactions, these are present even when the molecules do not possess permanent electric moments. These dispersional interactions cannot be dealt with on a classical electrostatics level owing to their relation to London s quantum dispersion theory, they have been termed London dispersional interactions. 

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