According to valence bond theory, what set of orbitals is used by a Period 4 metal ion in forming (a) a square planar complex; (b) a tetrahedral complex?

Understanding a square planar complex is essential in grasping how metal ions bond in certain geometries. These complexes typically involve transition metals and are characterized by a central metal ion surrounded by four ligands at the corners of a square plane.
Valence Bond Theory (VBT) helps explain the formation of these complexes by focusing on the hybridization of atomic orbitals.
In a square planar complex, the metal ion undergoes dsp^2 hybridization. This process involves:

• One 4d orbital
• One 4s orbital
• Two 4p orbitals

These orbitals mix to create four new hybrid orbitals oriented in a square plane. This geometry is common in d^8 metal ions such as Nickel(II), Palladium(II), and Platinum(II). The arrangement allows for maximum overlap between the metal and ligand orbitals, leading to a stable bond.

A tetrahedral complex is another key structure in coordination chemistry. In this geometry, a central metal ion is surrounded by four ligands at the corners of a tetrahedron.
Tetrahedral complexes are more common for smaller metal ions or those that can accommodate fewer ligands due to size constraints.
According to Valence Bond Theory, forming a tetrahedral complex involves sp^3 hybridization. This hybridization process includes:

• One 4s orbital
• Three 4p orbitals

By combining these orbitals, the metal ion forms four new hybrid orbitals pointing towards the corners of a tetrahedron. These complexes are seen with metal ions like Zinc(II) and Cadmium(II). The 109.5-degree bond angles between ligands help minimize repulsion, leading to a stable structure.

Hybridization is a fundamental concept in understanding the geometry of metal complexes. It describes the process where atomic orbitals combine to form new hybrid orbitals, which dictate the shape and bonding of the complex.
For a metal ion in a square planar complex, dsp^2 hybridization occurs. This involves mixing:

• One 4d orbital
• One 4s orbital
• Two 4p orbitals

forming four hybrid orbitals in a square planar arrangement.
In tetrahedral complexes, the metal ion undergoes sp^3 hybridization, mixing:

• One 4s orbital
• Three 4p orbitals

resulting in four hybrid orbitals in a tetrahedral arrangement.
Understanding hybridization helps predict the structure and stability of metal complexes. It's a vital part of learning how different orbital combinations influence the 3D arrangement of atoms and the overall chemistry of the complex.