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 ionizable. 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 ?
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