Number of chlorides satisfying secondary valency in CoCl₃.4NH₃
 

The species that fulfil the secondary valency are known as ligands in the current idea of coordination compounds, while the primary valency is the oxidation state of the central metal ion. Secondary valency has a definite orientation in space around the metal, whereas primary valency is non-directional. The amount of species that meet secondary valency provides the coordination a defined geometry. When a coordination molecule is ionised in aqueous medium, the species that fulfil the secondary valency cannot be produced in their free state, whilst the species that satisfy the primary valency may.