The kappa convention is used to specify which ligand atoms are bonding to the central atom and in polynuclear species which atoms, both bridged and unbridged, link to which central atom. For monodentate ligands there is no ambiguity as to which atom is forming the bond to the central atom. However when a ligand has more than one atom that can link to a central atom the kappa convention is used to specify which atoms in a ligand are forming a bond. The element atomic symbol is italicised and preceded by kappa, κ. These symbols are placed after the portion of the ligand name that represents the ring, chain etc where the ligand is located. For example:
*pentaamminenitrito-κO-cobalt(III) specifies that the nitrite ligand is linking via the oxygen atom
Where there is more than one bond formed from a ligand by a particular element a numerical superscript gives the count. For example:
* aqua[(ethane-1,2-diyldinitrilo-κN,)tris(acetato-κO)acetato]cobaltate(1-), the cobalt anion formed with water and pentadentate edta, which links via two nitrogen atoms and three oxygen atoms. There are two bonds from nitrogen atoms in edta which is specified by -κN,. The three bonds from oxygen are specified by tris(acetato-κO), where there is one ligation per acetate.
In polynuclear complexes the use of the kappa symbol is extended in two related ways. Firstly to specify which ligating atoms bind to which central atom and secondly to specify for a bridging ligand which central atoms are involved. The central atoms must be identified, i.e. by assigning numbers to them. (This is formally dealt with in the recommendations). To specify which ligating atoms in a ligand link to which central atom, the central atom numbers precede the kappa symbol, and numerical superscript specifies the number of ligations and this is followed by the atomic symbol. Multiple occurrences are separated by commas.
Examples:
: di-μ-chlorido-tetrachlorido-1κCl,2κCl-dialuminium, (aluminium trichloride).
:: tetrachlorido-1κCl,2κCl specifies that there are two chloride ligands on each aluminium atom.
:decacarbonyl-1κC,2κC,3κC-di-μ-hydrido-1:2κH;1:2κH-triangulo-(3  Os—Os), (Decacarbonyldihydridotriosmium).
::decacarbonyl-1κC,2κC,3κC shows that there are three carbonyl groups on two osmium atoms and four on the third.
::di-μ-hydrido-1:2κH;1:2κH specifies that the two hydride bridge between the osmium atom 1 and osmium atom 2.