Sodium molecule , application shell

The inertness of chromium (III) ion has allowed a complete characterization of the solvation of this ion in several mixed-solvent systems. For this inert transition metal ion of charge 3+, concern with the first shell coordination of solvent molecules can be viewed as a subdivision of coordination chemistry, a point of view less easily applicable to labile systems of metal ions with lower charge. Thus the approach used here is different from that used by A. K. Covington and co-workers (16) in their NMR studies of labile systems (e.g., sodium and cesium chlorides in water-methanol solutions (17)). 

The formation of reverse micelles and water-ln-oll (w/o) mlcroemulslons In liquid hydrocarbons using the surfactant sodium bis(2-ethylhexyl) sulfosucclnate (AOT) has been widely studied (2m3). In nonpolar liquid solvents, these molecular aggregates generally consist of 3- to 20-nanometer-dlameter, roughly spherical shells of surfactant molecules surrounding a polar core, which Is typically an aqueous solution. This combination of hydrophilic, hydrophobic, and Interfaclal environments In one solvent has created potential applications In separations (4.5), chromatography ( ), and catalytic reactions (2). 

The second term in the square brackets is the Born expression applicable at distances n + Ari, i.e., beyond the first hydration shell of thickness Ar. The first term describes the electrostatic interaction inside this shell, characterized by a relative permittivity e now, approximated by the square of the refractive index of water at the sodium D line. With the relevant de /rfT and de/tfT values for water at 25 °C, the enthalpy of hydrationEq. (2.28)is AHeh+A//ei2 = -69.5z2[(0.35(Ari/ri)+1.005)/(ri+Ari)] kJ mor The entropy is then A5eu + A5ei2 = —4.06z [(1.48(Ari/ri)+1.00)/(ri + Ari)] J mol The thickness of the first hydration shell, Ar, depends on the number of water molecules, hi, in it, the hydration number. According to the model (Marcus 1987) hi = 0.36 zi /(r/nm), that is, it is proportional to the charge number of the ion and inversely proportional to its radius. The volume occupied by hi water molecules is nhid l6, where cfw = 0.276 nm is the diameter of a water molecule. Hence the volume of the first hydration shell is given by ... 

We have extended application of the Hill formalism to poly-dentate ligands, polyamines competing with tetrahydrofuran for solvation of the sodium cation (118). The Hill plots obtained are no longer linear, denoting cooperativity. Entries of the first and of the second diamine molecules into the sodium coordination shell are independent and equiprobable steps Kj = K-j and K2 X. This permits also a direct determination of the chelate effect (118). 

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