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the association of molecules of a solvent with molecular, ionic, or particulate solute units. When the association involves water molecules, solvation is referred to as hydration.
Solvation results in the formation of solvates (hydrates), which are compounds of definite or, more often, indefinite composition. The molecules of the solvent are associated with the molecules or ions of the solvated substance through forces of various types and intensities, from weak forces of molecular interaction to the forces of chemical bonds. In solutions, the solvent molecules involved in solvation create spheres of solvation around the molecules or ions of solute.
A distinction is usually made between primary solvation, the interaction of molecules or ions of a substance with the closest molecules of solvent, and secondary solvation, the interaction of molecules or ions that have undergone primary solvation with more distant solvent molecules. When the solvation is complete, all the molecules of the solvent are associated with the spheres of solvation; that is, they enter the sphere of action of the force field of the molecules or ions of solute.
Solvation acts on the thermodynamic and other properties of the solution; it causes the electrolytic dissociation of electrolytes in polar solvents, the solubility of nonelectrolytes, and many liquid-phase chemical reactions. Solvation of molecules or ions of the surface layer is an extremely important factor in the stabilization of disperse systems having a high degree of dispersion in a liquid dispersion medium (sols, ladees, emulsions). Solvation may occur not only in a liquid solvent but also during the sorption by a substance of solvent vapors from a gaseous medium.
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L. A. SHITS