Why are complex ions of Zn+2 colorless?
Zn^+2 has the following electron configuration:
1s2 2s2 2p6 3s2 3p6 3d10.
All the electrons are paired. Often color comes from unpaired electrons.
Complex ions of Zn+2 are colorless because they do not have any d-electron transitions in their electronic structure. The color of a complex ion is determined by the arrangement of electrons and the energy difference between the different electronic states.
To understand this, we need to consider the electronic structure of zinc (Zn). Zn has a full d-orbital with no unpaired electrons, and thus, it has no d-d electron transitions. When a metal ion like Zn+2 forms a complex with ligands, the electrons from the ligands can form coordination bonds with the metal ion and create a new set of molecular orbitals.
In the case of Zn+2, the electronic configuration is [Ar] 3d10. Since all the d-orbitals are already fully occupied, there are no available d-electrons to undergo electronic transitions. As a result, complex ions of Zn+2 do not absorb visible light, and hence, they appear colorless.
This explanation is based on the principles of ligand field theory, which describes the splitting of d-orbitals in complex ions. By examining the electronic configuration and considering the arrangement of electrons, we can determine the color or lack thereof in complex ions.