Valence Bond Theory and Hybridization

The valence bond theory is a model used to explain the formation of chemical bonds in terms of overlapping atomic orbitals. According to this theory, atoms form bonds by overlapping their valence orbitals, which results in the sharing of electron pairs. The concept of hybridization arises from the need to explain the observed geometries of molecules.

Hybridization in Coordination Compounds

Coordination compounds are formed when a central metal atom or ion is surrounded by ligands. The ligands are Lewis bases that donate electron pairs to the metal atom, forming coordinate covalent bonds. In coordination compounds, the central metal atom/ion often undergoes hybridization to explain its geometry.

Hybridization in K2[Ni(CN)4]

In K2[Ni(CN)4], the central metal atom is nickel (Ni). To determine the hybridization of the central atom, we need to consider the electronic configuration and geometry of the compound.

- The electronic configuration of Ni is [Ar] 3d8 4s2.
- The compound has a square planar geometry.
- In a square planar geometry, the central atom is bonded to four ligands in a plane, with bond angles of 90°.

Application of Valence Bond Theory

According to the valence bond theory, the hybridization of the central metal atom is determined by the number and type of ligands attached to it. The hybridization of the central atom in K2[Ni(CN)4] can be determined as follows:

- The compound has four ligands (CN-) attached to the central Ni atom.
- Each CN- ligand donates a lone pair of electrons to form a coordinate covalent bond with Ni.
- The four ligands form sigma bonds with the Ni atom by overlapping their atomic orbitals.
- To accommodate the bonding and achieve the observed square planar geometry, the 3d, 4s, and 4p orbitals of Ni undergo hybridization.

Explanation of dsp2 Hybridization

In dsp2 hybridization, the central atom's 3d, 4s, and 4p orbitals combine to form five hybrid orbitals. These hybrid orbitals are directed towards the corners of a trigonal bipyramidal geometry, with three orbitals lying in the xy-plane and the other two perpendicular to it.

In the case of K2[Ni(CN)4]:
- The 3d and 4s orbitals of Ni combine to form three hybrid orbitals.
- The 4p orbitals of Ni remain unhybridized.
- The three hybrid orbitals form sigma bonds with three CN- ligands, resulting in trigonal planar geometry.
- The remaining two 4p orbitals of Ni form pi bonds with the remaining two CN- ligands, resulting in a square planar geometry.

Therefore, the hybridization of the central atom (Ni) in K2[Ni(CN)4] is dsp2.