Question

Explain the formation of ${\left[ {NiC{l_4}} \right]^{2 - }}$ on the basis of VBT.

Answer 1

Complex compounds contain a metal atom, ligands. These both are present in the coordination sphere. The hybridization is responsible for the geometry of the compound. The valence electrons play an important role in the formation of complex compounds.

Complete answer:
Complex compounds can also be known as coordination compounds. These compounds can retain their identity even dissolved in water or any other organic solvents. This is the special property of the complex compounds.
Valence bond theory is useful for the explanation of hybridization and hybrid orbitals based on the valence electrons of metal and the electrons were donated by ligand.
Nickel is the element with atomic number $28$ and chlorine is the element with atomic number $17$. Chlorine can act as a ligand and donates a lone pair of electrons.
The oxidation state of nickel is $x + 4\left( { - 1} \right) = - 2 \Rightarrow x = + 2$
Nickel exists as $N{i^{ + 2}}$ and has eight valence electrons. These eight electrons arranged in the $3d$ orbital. The coordination number of nickel is $4$.
As chlorine is a weak ligand, there is no pairing up of electrons. The s and p orbitals combine to form $4s{p^3}$ hybrid orbitals. Thus, the hybridization is $s{p^3}$.
Thus, the shape of tetrachloronickelate (II) ions is tetrahedral.

Note:
Though the hybridization and bonding of complex compounds can be known from the valence bond theory, it was not successful in explanation of magnetic properties. Though the unpaired electrons were known. The differentiation of weak and strong ligands can also not be known.