Cation polarizing power

Indication of an interaction with the cation is a cation-dependent frequency shift of the adsorbate band with reference to the gasphase purely vibrational transition. In the case of adsorbed CO the displacement of the main band apparently follows a direct cation-polarizing-power dependence (see Figure 12). Compared to zeolites X and Y [83] this shift is smaller on A-type zeolites, indicating an additional influence of the structure as well as the Si/Al ratio [84]. 

The curves shown in Fig. 11 are of some interest because the cation effect is the opposite of that which might be predicted from studies of the effects of cation polarizing power on the polymerization constants (Hess, 1971). Hess has pointed out that values of K tend to increase as the polarizing power of the cation (Z/r2) increases. Referring to the polymerization reactions ... 

The oxide activities shown in Fig. 11 for the Mg and Ca systems refer to a common (hypothetical) standard state value of Xq2- =1.0 for both systems so that the activities can be compared. Note that if either oxide fails to dissociate completely then Xq2-in the pure liquid oxide will be less than 1.0. The departure of X 2- from unity is likely to increase with cation polarizing power (cf. SiO ). 

Predict and explain periodic trends in the polarizability of anions and the polarizing power of cations (Section 2.13). 

Arrange the cations Rb" ", Be2+, and Sr23 in order of increasing polarizing power. Give an explanation of your arrangement. 

Rb+ < Sr2+ < Be2+. Smaller, more highly charged cations have greater polarizing power. 

Alcohols are hydroxylated alkyl-compounds (R-OH) which are neutral in reaction due to their unionizable (OH) group (e.g., methanol, ethanol, isopropanol, and w-butanol). The hydroxyl of alcohols can displace water molecules in the primary hydration shell of cations adsorbed onto soil-solid and sediment-solid clay particles. The water molecule displacement depends mainly on the polarizing power of the cation. The other adsorption mechanisms of alcohol hydroxyl groups are through hydrogen bonding and cation-dipole interactions [19,65],... 

Clay minerals behave like Bronsted acids, donating protons, or as Lewis acids (Sect. 6.3), accepting electron pairs. Catalytic reactions on clay surfaces involve surface Bronsted and Lewis acidity and the hydrolysis of organic molecules, which is affected by the type of clay and the clay-saturating cation involved in the reaction. Dissociation of water molecules coordinated to surface, clay-bound cations contributes to the formation active protons, which is expressed as a Bronsted acidity. This process is affected by the clay hydration status, the polarizing power of the surface bond, and structural cations on mineral colloids (Mortland 1970, 1986). On the other hand, ions such as A1 and Fe, which are exposed at the edge of mineral clay coUoids, induce the formation of Lewis acidity (McBride 1994). 

Many nonionic organic contaminants require extreme acid conditions to accept H+ ions. In clays, the extent of protonation is related to the electronegativity and polarizing power of structural metal cations, in the order H+ > Al + > Fe > Mg +... 

The simplest approach to describing the interactions of metal cations dissolved in water with solvent molecules is the Born electrostatic model, which expresses solvation energy as a function of the dielectric constant of the solvent and, through transformation constants, of the ratio between the squared charge of the metal cation and its effective radius. This ratio, which is called the polarizing power of the cation (cf Millero, 1977), defines the strength of the electrostatic interaction in a solvation-hydrolysis process of the type... 

Figure 8.14 Effect of polarizing power on degree of hydrolysis of cations in water. Reprinted from D. R. Turner, M. Whitfield, and A. G. Dickson, Geochimica et Cosmochimica Acta, 45, 855-881, copyright 1981, with kind permission from Elsevier Science Ltd., The Boulevard, Langford Lane, Kidlington 0X5 1GB, UK.

Figure 8.16 shows how the complexing constants of ions vary with the polarizing power of the cation, ligand being equal. Note also here that the abscissa... 

Alkali metal salts of tris-maleato-ferrate(III) are high spin the isomer shifts of their Mossbauer spectra reflect the electronegativity and polarizing power of the cations. ... 

The consideration of these problems (138, 187) lead us to the conclusion that the polarizing power of the cations as measured by the effective nuclear charge alone, is most probably the influential parameter necessary to understand these effects. The polarizing power given otherwise as formal charge/radius or formal charge/radius or even better, effective nuclear charge/radius, cannot explain these effects as well. 

Tellurium hexafluoride itself has been found to form complexes with potassium, rubidium and cesium fluorides. The cesium compound has a stochiometry approaching Cs2TeF8 and, in these types of complexes, the stability of the lattice appears to be inversely related to the polarizing power of the cation and the compounds are only stable in the solid state.41 Several heptafluorotellurates(VI) have been prepared from the reaction of tellurium with chlorine trifluoride in anhydrous hydrofluoric acid followed by addition of the metal fluoride.42... 

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