Werner’s co-ordination theory-primary valency-secondary valency.

Werner’s co-ordination theory .

Alfred Werner’s expressed his famous co-ordination theory about the chemical bonding in complex compounds .

This theory explained the formation of complex compound , chemical bonding in complex compound , nature and three dimensional structure of complex compound successfully .

The main points of Werner’s co-ordination theory is as follows ,

( I ) The central metal or ion in each co-ordination compound has two type valency , namely primary valency or ionisable valency and secondary valency or non-ionisable valency .

( II ) The primary valency of the central metal atom or ion is satisfied by the anions . The oxidation number of central metal atom or ion is expressed by the primary valency .

( III ) The secondary valency of the central metal atom or ion is satisfied by the anion , neutral molecule or even by the cation .

( IV ) The number of secondary valency for a specific metal atom or ion is fixed . This specific value of secondary valency of the concern atom or ion is called co-ordination number .

(V ) The central metal atom or ion along with Ligand forms the co-ordination sphere .

( VI ) The geometry of the complex compound or ion in three dimensional space depends on the co-ordination number of that central metal atom or ion .

For examples, the central metal ion with co-ordination number ‘6’, shows octahedral geometry. Such as [ Co(NH3) 6 ] 3+ , [ Fe ( CN )6 ] 4- etc .

Again the central metal ion with co-ordination number ‘4’ shows tetrahedral or square planar geometry . Such as , [ Ni ( CO ) 4 ] , [ PtCl4 ] 2- etc .

( VII ) The anions which satisfy the primary valency of central metal atom or ion is expressed out side the third bucket . This sphere is called ionization sphere .

What is primary valency ?

In complex compound, the central metal atom or ion has type of valency . Now, the valency of central metal atom or ion which satisfied by the anion , is called primary valency .

Why primary valency is also known as ionic valency ?

The primary valency is ionisable .That is, in aqueous solution ,the anions are separated from the central metal atom or ion .

Consequently, primary valency is also called ionic valency .

What is secondary valency ?

In complex compound, the central metal atom or ion has type of valency .

Now, the valency of central metal atom or ion which satisfied by the anion , neutral molecule or by the cation with donor atom , are called secondary valency .

These anion , neutral molecule or cation which satisfy the secondary valency of the central metal ion are called Ligand .

Why primary valency is also known as non-ionic valency ?

The secondary valency is non-ionisable .That is, in aqueous solution , they does not separated from the central metal atom or ion .

Consequently, secondary valency is also called non-ionic valency .

Summary:

Werner’s co-ordination theory .

What is primary valency ?

What is secondary valency ?

Why primary valency is also known as ionic valency ?

Why primary valency is also known as non-ionic valency ?