Question

The secondary valency of platinum in tetra-ammine dichloro platinum (IV) chloride is:
A. \[ + 4\]
B. \[ + 2\]
C. \[3\]
D. \[6\]

Answer 1

Hint: Werner’s theory is the basis to find the secondary valency. Based on this theory, secondary valency is referred to the coordination number of metal ions or atoms. Coordination number is the total number of nearest atoms to the central atom.

Complete step by step solution:
A coordination compound is a compound which has coordinate bonds between the central atom and the neighbouring atoms or groups. Coordinate bond is a bond in which both electrons come from the same atom. There are different kinds of theories based on coordination compounds. Basic theory is Werner’s theory. Main postulates were:
Every metal has a primary valency and a secondary valency.
Primary valency is referred to the oxidation state of the metal ion.
Secondary valency represents the coordination number of the metal ion.
Molecules having secondary valencies are called ligands.
Secondary valencies are directional and primary valencies are non-directional in nature.
The compounds in which the ligands share the unshared pair of electrons to the central atom are called coordination compounds.
From this theory, we can calculate the secondary valency by finding the number of neighbouring ligands to the central atom.
Tetra-ammine dichloro platinum (IV) chloride is represented as \[\left[ {{\text{PtC}}{{\text{l}}_2}{{\left( {{\text{N}}{{\text{H}}_3}} \right)}_4}} \right]{\text{C}}{{\text{l}}_2}\]. Here the central atom is linked with two chlorine atoms and four ammonia groups. Therefore the coordination number is equal to \[2 + 4 = 6\]. Since secondary valency corresponds to the coordination number, it is also equal to 6.
Hence option D is correct.
Additional information:
It failed to explain why all elements cannot form coordination compounds. The directional properties of bonds were not explained. The color, magnetic properties and optical properties were also not explained.

Note: Werner’s theory could explain the cause of optical and geometrical isomerism of some compounds. Coordination compounds have a definite geometry. This is because the secondary valencies directed towards a fixed position in space.