solvation

Solvation is the interaction of solvent molecules with a solute, resulting in a solute being surrounded and stabilized by the solvent. In solution, solvent molecules organize around solute species to form a solvation shell; the first solvation shell is directly in contact with the solute and governs much of the short-range stabilization. Interactions include ion–dipole and dipole–dipole forces, hydrogen bonding, and van der Waals contacts. The extent and nature of solvation depend on solvent polarity, dielectric constant, and structure, as well as the solute’s charge, polarity, and size.

Thermodynamically, solvation is described by the Gibbs free energy of solvation, ΔG_sol, which combines enthalpic and entropic contributions (ΔG_sol = ΔH_sol − TΔS_sol). For ions, solvation energies are often discussed using continuum models such as the Born model, which treats the solvent as a dielectric continuum; more detailed predictions use explicit-solvent simulations or mixed approaches. Solvation can be enthalpically favorable, entropically favorable or unfavorable depending on solvent organization and solute release of solvent molecules.

Solvation and dissolution are related but distinct concepts. Solvation refers specifically to solvent–solute interactions that stabilize solute species; dissolution describes the formation of a homogeneous phase. In water, solvation is called hydration. Solvation is central to many chemical processes, influencing solubility, reaction mechanisms and rates, spectroscopy, and electrochemistry. In biology, solvent effects shape protein folding and biomolecular interactions. Modeling solvation ranges from implicit continuum descriptions to explicit molecular simulations.