Question

What are the primary and secondary valencies of copper in tetra ammine copper $II$ sulphate $\left[ {Cu{{\left( {N{H_3}} \right)}_6}} \right]S{O_4}$.

Answer 1

Hint: Primary valency is the oxidation state of the central metal atom while secondary valency is equal to the coordination number of the central metal atom. Primary valency is satisfied mainly by its ionization only. Secondary valency is satisfied by coordination sphere only.

Complete answer:
Since the primary valency of a coordination compound is the oxidation state of the central metal atom to which the ligands are attached. Now in the given compound , Tetraamminecopper $II$ sulphate, $\left[ Cu{{\left( N{{H}_{3}} \right)}_{6}} \right]S{{O}_{4}}$ the central metal atom is copper. Thus for primary valency we have to find the oxidation state of copper.
Also for finding oxidation the compound can be dissociated as:
${{\left[ Cu{{\left( N{{H}_{3}} \right)}_{6}} \right]}^{+2}}$ and $S{{O}_{4}}^{-2}$
Since ammine is a neutral ligand having no charge on it . We can take its charge as zero.
Therefore,
Oxidation State
$\text{+2 = x + 0}\left( 4 \right)$
$\text{x = +2}$
Hence the oxidation state of copper comes out to be $\text{ +2}$ . Therefore primary valency is $\text{ 2}$ .
The secondary valency of a metal atom in a coordination compound is the coordination number of the central metal atom. Also coordination number is the number of ligands that surrounds the central metal atom . Thus on looking the structure of the compound we can see that $4$ ammonia ligands are attached to central metal atom . Thus the coordination number of central metal atom is $4$ . Now we can say that its secondary valency is $4$ .
Therefore the primary and secondary valencies of Tetraamminecopper $II$ sulphate are $\text{ 2}$ and $4$.

Note:
The secondary valency of the central metal atom is mostly satisfied by ligands which may be neutral or negative ions . We can find the oxidation state without dissociating the compound too. We should talk about valency of other atoms while calculating for central metal atoms.