Write any two postulates of Werner's theory of co-ordination compounds.

Explanation

(a) 1. In coordination compounds, metal posses two types of valences.
(i) The primary valence.
(ii) The secondary valence
2. The primary valence is ionisable wDhereas, the secondary valence is non-ionisable.
3. The primary valence is variable whereas, the secondary valence is fixed.
4. Primary valence are satisfied by negative ions whereas secondary valence are satisfied by negative ions or neutral molecules (ligands)
5. The secondary valences are directed towards fixed position in space around the central ion.
6. The primary valence corresponds to oxidation state of central metal atom and secondary valence corresponds to coordination number.
(b) Linkage Isomerism
(b) Type of isomerism in `[Co(NH_(3))_(5)SCN]Cl_(2)` and `[Co(NH_(3))5NCS]Cl_(2)` complex compounds.
These show linkage isomerism as central metal atom .cobalt. is bonded through S-atom of SCN while with N-atom of NCS in other case.
In other words .SCN. and .NCS. are ambidentate ligands. These have two donor atoms (S-taoms and N-atom respectively).