Give a detailed note on comparison of the elements of first transition series with second and third transition series with special reference to magnetic property, spectral property, metal-metal bonding and cluster compounds (elementary approach).
Answers
the first transition series, 3d orbitals are progressively filled whereas, in second and third transition series, 4d and 5d orbitals are filled.
(ii) Oxidation states
+2 and +3 oxidation states of first transition series elements are more stable than +2 and +3 oxidation states of second and third transition series elements. Cobalt forms several complexes with +2 and +3 oxidation states but no such complexes are known for Rh,Ir which belong to the same group to which Co belongs. The maximum oxidation state in a group increases from first transition series to third transition series. In group 8, iron shows +2 and +3 oxidation states and ruthenium and osmium show +4, +6 and +8 oxidation states.
(iii) Ionization enthalpies
5d series elements have higher ionization enthalpies than 3d and 4d series elements. In 5d series, 4f orbitals are filled which have poor shielding effect and valence electrons experience higher effective nuclear charge. This results in higher ionization enthalpies for 5d series elements.
(iv) Atomic sizes
4d series elements have higher atomic size than 3d series elements.
4d and 5d series elements have nearly same atomic size due to lanthanoid contraction.