Geochemical reactions commonly fall into two classes: (1) ligand exchange reactions where one of the atoms bonded to a metal is exchanged for another and (2) electron exchange reactions where the valence state of a metal changes. Electron exchange reactions cannot be understood without first addressing the role of the coordinated ligands, and we review the use of small aqueous oligomers and complexes to understand mechanisms of ligand exchange reactions at the surfaces of minerals such as metal-(hydr)oxides in soil.