Enlist the main postulates of Werner's theory.

(N/A) The main postulates of Werner's theory are:
$1$. In coordination compounds,metals exhibit two types of linkages or valencies: primary and secondary.
$2$. Primary valencies are normally ionisable and are satisfied by negative ions.
$3$. Secondary valencies are non-ionisable.
$4$. Secondary valencies are satisfied by neutral molecules or negative ions. The secondary valency is equal to the coordination number and is fixed for a metal.
$5$. The ions/groups bound by secondary linkages to the metal have characteristic spatial arrangements corresponding to different coordination numbers. Such a spatial arrangement is called a coordination polyhedron.
$6$. Octahedral,tetrahedral,and square planar geometrical shapes are common in coordination compounds of transition metals.
For example:
Octahedral complexes: $[Co(NH_3)_6]^{3+}, [CoCl(NH_3)_5]^{2+}, [CoCl_2(NH_3)_4]^{+}$
Tetrahedral complex: $[Ni(CO)_4]$
Square planar complex: $[PtCl_4]^{2-}$
The species within the square bracket are coordination entities or complexes,and the ions outside the square bracket are called counter ions.