Editing Chemical reaction (section)

===Complexation===
[[File:Ferrocene-from-xtal-3D-balls.png|160px|thumb|[[Ferrocene]] – an iron atom sandwiched between two C<sub>5</sub>H<sub>5</sub> [[ligand]]s]]
In complexation reactions, several [[ligand]]s react with a metal atom to form a [[coordination complex]]. This is achieved by providing [[lone pair]]s of the ligand into empty [[Atomic orbital|orbitals]] of the metal atom and forming [[dipolar bond]]s. The ligands are [[Lewis base]]s, they can be both ions and neutral molecules, such as carbon monoxide, ammonia or water. The number of ligands that react with a central metal atom can be found using the [[18-electron rule]], saying that the [[valence shell]]s of a [[transition metal]] will collectively accommodate 18 [[electron]]s, whereas the symmetry of the resulting complex can be predicted with the [[crystal field theory]] and [[ligand field theory]]. Complexation reactions also include [[ligand exchange]], in which one or more ligands are replaced by another, and redox processes which change the oxidation state of the central metal atom.<ref>[[#Wiberg|Wiberg]], pp. 1180–1205</ref>