page_title: Coordination number
section_title: Molecules, polyatomic ions and coordination complexes
hierarchical_section_title: Coordination number / Molecules, polyatomic ions and coordination complexes
caption_attribution_description: English: structure of the chemical compound Ph3PAuCl
context_page_description: In chemistry, crystallography, and materials science, the coordination number, also called ligancy, of a central atom in a molecule or crystal is the number of atoms, molecules or ions bonded to it. The ion/molecule/atom surrounding the central ion/molecule/atom is called a ligand. This number is determined somewhat differently for molecules than for crystals.
  For molecules and polyatomic ions the coordination number of an atom is determined by simply counting the other atoms to which it is bonded. For example, [Cr(NH₃)₂Cl₂Br₂]⁻ has Cr³⁺ as its central cation, which has a coordination number of 6 and is described as hexacoordinate. The common coordination numbers are 4, 6 and 8.
context_section_description: In chemistry, coordination number (C.N.), defined originally in 1893 by Alfred Werner, is the total number of neighbors of a central atom in a molecule or ion. The concept is most commonly applied to coordination complexes.
caption: Chloro(triphenylphosphine)gold(I), which features 2-coordinate metal centre.
exif: {}