Question

Explain the following:
$\left(i\right)$ Why do transition metal ions possess a great tendency to form complexes?
$\left(ii\right)$ The paramagnetic character in $3d$-transition series elements increases upto $Mn$ and then decreases.

Answer 1

(i) The transition metal ions possess a great tendency to form complexes because of their small size, high ionic charge and availability of partially filled d-orbitals for bond formation. These partially filled d-orbitals can easily accomodate ligands electrons and consequently transition metals ions form complexes. Examples ${\left[Fe{\left(CN\right)}_6\right]}^{3-},Ni{\left(CO\right)}_4$ etc.
(ii) In the $3d$ transition series as we move from $Sc$(21) to $Mn$(25), the number unpaired electrons increases and hence paramagnetic character increases. After $Mn$, the pairing of electrons in the d-orbital starts and the number of unpaired electrons decreases and hence, paramagnetic character decreases.