Solved Examples on Transition Elements:

Question:1, Ti(H₂O)₆]³⁺ is coloured whereas  [Sc(H_­2O)₆]³⁺ is colourless, though it is a transition metal complex. Explain the observation.

Solution: Ti³⁺ has one electron in the d-orbital (3d¹) which can absorb energy corresponding to yellow wavelength and jump from lower energy level to higher energy level. But Sc³⁺ has no electron in d-orbital.

Question: 2, NiCl₄]^2– is paramagnetic while (Ni(CO)₄] is diamagnetic. Why?

Solution: In [Ni(CO)₄], Ni is in zero oxidation state whereas is (NiCl₄]^2–, Ni is in +2 oxidation state. In the presence of ligand CO, the unpaired electrons of Ni pair up but Cl^– being a weak ligand is unable to pair up the unpaired electrons.

Question:3, Calculate the magnetic moment of V³⁺.

Solution: The electronic configuration of V³⁺ is [Ar] 4s°3d². In the d–orbitals there are 2 unpaired electrons 

Question:4, Why Sm²⁺, Eu²⁺ and Yb²⁺ ions in solutions are good reducing agents but an aqueous solution of Ce⁴⁺ is a good oxidizing agent?

Solution: The most stable oxidation state of lanthanides is +3 hence ions in +2 state tend to change to +3 state by loss of electron and those in+4 state tend to change to +3 state by gain of electron