Neutron and X–ray scattering studies of hydration in aqueous solutions

The presence of ions and/or apolar species in water provides a rich and varied environment in which many natural processes occur. This review provides results of recent structural studies of aqueous solutions derived from state–of–the–art neutron and X–ray scattering methods. The enhanced resolution provided by methods such as neutron diffraction and isotopic substitution, and anomalous X–ray diffraction, have given scientists new insights into the contrasting hydration structures of a variety of ions and small molecules, and crucially into how these structures might affect the general properties of solutions. The discussion points out common features of ionic hydration within particular series, such as the alkalis, halides and transition metals, and also indicates where significant differences in hydration structure appear.