Sodium ion solvation

A sodium ion solvated by molecules of the protic solvent water... 

A similar reasoning may explain the difference in reactivities of the lithium and sodium ion-pairs in THF. The larger ionic radius of the sodium than that of the lithium cation, favoring the formation of loose pairs, makes the sodium pair much more reactive than the lithium salt at lower temperatures. However, at higher temperatures the sodium salt becomes less reactive than the lithium salt as it looses its solvation more readily than the latter. 

Fig. 13 Results from the quantum calculations on the duplex sequence 5 -GAGG-3. In a, the sodium ions and their solvating water molecules are located at positions near the phosphate anions of the DNA backbone. In b, one sodium ion is moved from near a phosphate anion to N-7 of a guanine, which molecular dynamics calculations show to be a preferred site. The balloons represent the hole density on the GAGG sequences with the two different sodium ion orientations. The radical cation clearly changes its average location with movement of the sodium ion...

When sodium hydroxide dissolves in water, the result is a solution containing solvated sodium ions and solvated hydroxide ions. 

Water molecules are absent from the hydrophobic interior, but both the choline and the phosphate headgroups are fully solvated [41]. Similarly, the first hydration shell of the sulfate headgroup of SDS is formed rather by water molecules than by sodium ions. Because of hydration the charge density due to the lipid headgroups is overcompensated by the water dipoles, thereby reducing the transmembrane potential by 50-100 mV across the lipid water interface and resulting in a negative potential at the aqueous side [42]. 

The strength of metal ion solvation affects not only the half-wave potentials but also the rates of electrode reactions of metal ions. For the reduction of a given metal ion, the reaction rate tends to decrease with increasing strength of solvation. The linear relation in Fig. 8.5 was obtained for the reduction of a sodium ion AG°v(Na+) is the solvation energy of Na+ and ks is the standard rate constant at the formal potential [23 a].2 For alkali metal ions in the same solvent, the rate... 

The solvation numbers of ions such as Mg2+, Al3+, and Be2+ may be determined by low temperature PMR techniques as mentioned earlier. The solvation number for small spherical ions may be determined in certain circumstances using a titration technique suggested by Van Geet (15). It is based on the competition by water for the solvation sphere of sodium ions in tetrahydrofuran (THF) measured by Na shifts. The salt must contain a large anion, which is assumed to be unhydrated during the titration otherwise a sum of hydration numbers would be determined. The assumptions made by Van Geet are basically those of the present treatment. His apparent constant is for the reverse of the equilibrium of Equation 21 and can be identified as l/K[P]p, where [P]f is the free THF concentration, effectively constant in the early stages of the titration. 

Reduction of the hydrocarbon 5,6,11,12-tetraphenyltetracene (rubrene) with a sodium mirror in THF gave a dark green solution from which almost black crystals of the tetrakis-sodium salt 83 could be obtained.1353 Two of the four sodium cations (each doubly solvated by THF) are located (Fig. 53) above and below the central tetracene skeleton and the other two are between pendant phenyl groups. The central sodium ions are 8-coordinate with Na-C 260-263 pm to the phenyl-substituted and 272 pm to the other... 

Na <=4 —0 + Na) in the radical anion in the absence of excess diphenylmethanone Why [Notice that there is no 23Na splitting of the electron resonance of sodium naphthalenide in 1,2-dimethoxyethane, but such splittings are observed in oxacyclopentane (tetrahydrofuran) see Sections 8-7F and 15-11E for discussion of possible differences between solvents in their ion-solvating powers.]... 

In solvating a charged species, a solvent disperses the charge over a larger area, which lowers the energy of the system. For example, when a sodium ion is dissolved in water, the positive charge on the sodium is dispersed among many water molecules. This is shown schematically in 4. 

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