Solvation shell monovalent ions

The secondary solvation shell about an ion can be studied by neutron diffraction and incoherent neutron scattering.When applied to 5 m LiCl, these methods, indicate that Li" " does not have a secondary solvation shell. The same result would be expected for larger inorganic monovalent cations. The absence of a secondary solvation shell around monovalent ions is not surprising given the relatively small values of T, and T. quoted... 

Cations adsorbed on the basal planes of smectites can be immobilized in two kinds of surface complex (4). The surface complex is inner-sphere if the cation is bound directly to a cluster of surface oxygen ions, with no water molecules interposed, and it is outer-sphere if one or more water molecules is interposed between the cation and the siloxane surface to which it binds 30). Thus, adsorbed cations in outer-sphere surface complexes retain solvation shells, whereas those in inner-sphere surface complexes can at most be only partially solvated. Spectroscopic data 31) suggest that monovalent cations in inner-sphere surface complexes remain immobilized on a timescale of ca. 100 ps, whereas those in outer-sphere surface complexes are able to diffuse along the siloxane surface over this timescale. 

While Bom assumes that the dielectric response of the solvent is linear, nonlinear effects such as dielectric saturation and electrostriction should occur due to the high electric field near the ion. Dielectric saturation is the effect that the dipoles are completely aUgned in the direction of the field so that any fiuther increase in the field cannot change the degree of ahgnment. Electrostriction, on the other hand, is defined as the volume change or compression of the solvent caused by an electric field, which tends to concentrate dipoles in the first solvation shell of an ion. Dielectric saturation is calculated to occur at field intensities exceeding 10 V/cm while the actual fields around monovalent ions are on the order of 10 V/cm. ... 

This is a term inversely proportional to the hydrated ion radius that involves the supposedly tight-held first solvation shell. The charge is omitted, since in this work we consider only monovalent anions. It is tacitly assumed that all ions feel a similar dielectric environment within the monolayer, (b) A contribution from the cavity term that involves nonpolar ion-solvent interactions. This is consistently modelled as proportional to solute area or volume. 

The monovalent thallium ion, with its relatively large ionic radius (1.50 A for a 6-coordinate ion), has only weak electrostatic interactions with its ligands. The valence-shell electronic configuration of d s with a lone pair makes the covalent interactions weak as well. Overall, the thallium ion is weakly solvated in most solvents, and crystallizes even without any coordinated solvent molecules. Thallium(I) compounds are the most widely explored group among thallium derivatives. The T1+ state is also the most stable ion in aqueous solutions. 

For small monovalent and polyvalent ions, the effect will produce a shell of oriented water molecules bound to the ion, with the orientation favoring 9 = 0° for cations and 180° for anions. The surrounding shell of water molecules thus formed constitutes the waters of solvation or hydration of the ion. The number of water molecules associated with an ion (its hydration number ) is characteristic of that ion but normally ranges between 4 and 6. Waters of hydration are not completely and irreversibly bound to a given ion, of course. They are slowly (on a molecular timescale), but continually exchanged for other bulk water molecules. 

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