Polarization of charges

The average cloud is spherically synnnetric with respect to the nucleus, but at any instant of time there may be a polarization of charge givmg rise to an instantaneous dipole moment. This instantaneous dipole induces a corresponding instantaneous dipole in the other atom and there is an interaction between the instantaneous dipoles. The dipole of either atom averages to zero over time, but the interaction energy does not because the instantaneous and induced dipoles are correlated and... 

The electrostatic behavior of intrinsically nonconductive substances, such as most pure thermoplastics and saturated hydrocarbons, is generally governed by chemical species regarded as trace contaminants. These are components that are not deliberately added and which may be present at less than detectable concentrations. Since charge separation occurs at interfaces, both the magnitude and polarity of charge transfer can be determined by contaminants that are surface active. This is particularly important for nonconductive liquids, where the electrostatic behavior can be governed by contaminants present at much less than 1 ppm (2-1.3). 

Honciuc A, Otsuka A, Wang Y-H, McElwee SK, Woski SA, Saito G, Metzger RM (2006) Polarization of charge-transfer bands and rectification in hexadecylquinolinium 7,7,8-tricyanoquinodimethanide and its tetrafhioro analog. J Phys Chem B110 15085-15093... 

Graf (G8) measured the pressure buildup due to electrostatic charging of stationary drops. He found this pressure to be some 30-60% of the value given by Eq. (4), independent of polarity of charge or dielectric constant of the liquid. This factor, which he terms a charging factor, was a function of both geometry and liquid properties. It may also reflect polarization effects that are neglected in Eq. (4). 

The chemical shifts obtained in solution under different experimental conditions were compared to the shifts of the TMEDA complexes in the solid state. For 6, all data indicate a triplet structure of the CIP. The most compelling evidence for the triplet structure is the polarization of charge towards the two bridging carbons under CIP conditions. However, for 7, the charge distribution differs under CIP conditions in solution and in the solid state, as reflected by the chemical shifts. In solution, the shift data indicate again a triplet structure. In the solid state, however, the cations are not located at the bridging carbons, but shifted towards the five-membered ring systems. 

Since P = %E (Equation (10)), 4tuxE is the internal electric field created by the induced displacement (polarization) of charges. Usually, the induced polarization causes the spatial orientation of the internal electric field to differ from the applied electric field and, like ay (co), xij( ) is a tensor quantity that reflects the anisotropy of the internal electric field. 

To use electrical response to determine property surface information as discussed in the next section, or simply how to evaluate property changes associated with polarization of charge distributions, full electrical analysis is crucial. 

Although Lewis structures of this type are not entirely adequate descriptions of the excited states, they do correspond to the MO picture by indicating polarization of charge and the presence of polar radical-like centers. In addition to the increased energy content, the high reactivity of the excited states is associated with the presence of half-filled orbitals. The two SOMO orbitals in the excited states have enhanced radical, cationic, or anionic character. 

It follows then that as the electrical field intensity increases across a dielectric, the stiffness or the elastance of the dielectric increases. This comes about by physical compaction of the particles in the diffuse layer and by strong orientation of the dipoles or the polarization of charges in the compact layer. Hence, as the electrical field intensity is increased by compression of DDL, the capacitance of the system decreases due to polarization. An example of a similar behavior has been shown in thin electrolyte films between silica surfaces, where the dielectric permitiv-ity decreases with increasing electrolyte concentration, resulting in increasing field strength across the thin film (Israelachvili and Adams, 1978 Pashley, 1981 Basu, 1993). 

Finkelstein, E.I. Chao, P.G. Hung, C.T. Bulinski, J.C. Electric field-induced polarization of charged cell surface proteins does not determine the direction of galvanotaxis. Cell Motil. Cytoskel. 2007, 64 (11), 833-846. 

This is displacement of positive ions with respect to negative ions. To clarify the division between electronic and ionic polarization electronic polarization is the displacement of the electron cloud with respect to the nucleus ionic polarization is the displacement of ions relative to each other. The hydrated sheath around an ion at rest is symmetrical (not really at rest, everything is bumping around at room temperature, we are talking statistically). When current flows, the sheath will lag behind the migrating ion, and the sheath is no longer symmetrical to the ion, cf. the Wien effect (Section 8.4.1). This is local polarization of charges bound to each other. 

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