solvation
/ sol-VAY-shun /
Drop a sugar cube into hot tea and stir: the cube shrinks and vanishes as the liquid molecules swarm in, surround each piece, and carry it off. Every dissolved particle ends up wrapped in a snug coat of solvent molecules. That wrapping-up — solvent molecules clustering around and embracing each dissolved particle — is solvation.
Solvation is the process by which solvent molecules surround and interact with the particles of a dissolved substance, forming a shell of solvent around each ion or molecule. When the solvent is water, it is called hydration. The solvent molecules orient themselves to maximize favorable attractions — ion–dipole forces around an ion, hydrogen bonds around a polar molecule — and the energy released by this embrace (the solvation energy) is what helps pry the solute apart and keep it dissolved.
Why it matters: solvation is the heart of why things dissolve at all; whether a substance dissolves depends on whether solvation pays back the energy cost of breaking the solute and solvent apart. The honest caveat is that solvation is not the same as dissolving: dissolving is the whole journey from solid to solution, while solvation is specifically the step where solvent molecules cloak each freed particle.
When copper sulfate dissolves, each copper ion gets wrapped in six water molecules that point their oxygen ends toward it — and this hydration is what gives the solution its blue color.
Solvent molecules form an organized shell around each dissolved particle.
Solvation (the embrace by solvent) is one step inside dissolving (the whole process). Hydration is just solvation when the solvent is water. Strong solvation can make dissolving release heat, while weak solvation can make it absorb heat — which is how instant cold packs work.