Terminology

 

The important terms used in the study of coordination compounds are mentioned below.

 

Central Metal Ion

It is an acceptor atom containing vacant orbitals to which a fixed number of ligands are attached via co-ordinate bonds in definite geometrical arrangement.

 

Co-ordination Sphere

Complex ion enclosed in square bracket, it behaves as a single unit.

 

Ionization Sphere

Part of compound present outside co-ordination sphere, e.g

Co-ordination Number

It is the total number of ligands attached to the central metal atom through co-ordinate bonds or the number of atoms of a ligand attached to the same central atom, e.g. hexadentate ligand should be counted as forming six co-ordinate bonds.
 

Oxidation Number

It is the charge which the central atom appears to have if all the ligands are removed along with the electron pairs that are shared with the central atom.

                [Cr(H₂O)₄Cl₂]⁺

                x + (4 × 0) + (-1 × 2) = +1    [because the ligand H₂O is neutral and 2Cl^– carries - 2 charge]

                x + 0 - 2 = +1

                x = 3

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