Complex ions are examples of Lewis acid-base adducts and comprise central metal atoms or ions acting as Lewis acids bonded to molecules or ions called ligands that act as Lewis bases. A Lewis acid is a species that can accept an electron pair, whereas a Lewis base has an electron pair available for donation to a Lewis acid.

The equilibrium constant for an equilibrium involving the precipitation or dissolution of a slightly soluble ionic solid is called the solubility product, K sp , of the solid. For a heterogeneous equilibrium involving the slightly soluble solid M p X q and its ions M m+ and X n-

complex ion — ion consisting of a central atom surrounding molecules or ions called ligands via coordinate covalent bonds. ligand — molecule or ion acting as a Lewis base in complex ion formation; bonds to the central atom of the complex. Lewis acid-base adduct — compound or ion that contains a coordinate covalent bond between a Lewis acid and a Lewis base. Lewis acid — any species that can accept a pair of electrons and form a coordinate covalent bond.