Solvation shell

Solvation shell is a shell of any chemical species acting as a solvent, surrounding a solute species.

A classic example is water molecules solvating a metal ion. The electronegative oxygen atom contained in the water molecule attracts electrostatically to the positive charge on the metal ion. The result is a 'solvation shell' of water molecules surrounding the ion. This shell can be several molecules thick, dependent on the charge of the ion.

With other solvents and solutes, varying steric and kinetic factors can also affect the solvation shell. It is a very useful concept in Biochemistry.