Question

What is the primary and secondary valence of $PtC{l_2}.2N{H_3}$?

Answer 1

Recall the Werner’s theory for coordination compounds. He was the first to propose the concept of primary valence and secondary valence for a metal ion in the coordination complexes. The primary valences are satisfied by the negative ions and the secondary valence is equal to the coordination number.

Complete step by step answer:
In 1898, Werner proposed his theory of coordination complexes. The main postulates are:
1. In coordination compounds, metals show two types of linkages or valences – primary and secondary.
2. The primary valences are generally ionisable and are satisfied by negative ions .
3. The secondary valences are non-ionisable. These are satisfied by neutral molecules or negative ions. The secondary valence is equal to the coordination number and is fixed for a metal.
4. The groups/ions bound by the secondary valences to the metal have characteristic spatial arrangements corresponding to different coordination numbers.
In the given coordination compound that is, $PtC{l_2}.2N{H_3}$, Pt is the central metal ion which is bonded to 4 ligands that are, 2 Cl and 2 NH3. Thus, its coordination number is 4 and hence, secondary valence is equal to 4. Primary valence is zero because no ionisable ions are there in the given coordination compound.

Note: Alfred Werner, a Swiss chemist, was the first to formulate his own ideas about the coordination complexes. He prepared a large number of coordination compounds and studied their physical and chemical properties. Primary valence is also called an ionisable valence and secondary valence is also called a non-ionisable valence.