coordination number

https://doi.org/10.1351/goldbook.C01331
  1. The @C01329@ number of a specified atom in a @CT01038@ is the number of other atoms directly linked to that specified atom. For example, the @C01329@ number of carbon in methane is four, and it is five in protonated methane, CH5+. (The term is used in a different sense in the crystallographic description of ionic crystals.)
    Source:
    PAC, 1994, 66, 1077. (Glossary of terms used in physical organic chemistry (IUPAC Recommendations 1994)) on page 1100 [Terms] [Paper]
  2. In an inorganic @C01330@, the number of σ-bonds between @L03518@ and the @C00930@. π-bonds are not considered in determining the @C01329@ number.
    Source:
    Red Book, 3rd ed., p. 146 [Terms] [Book]