Compare the general characteristics of the first series of the transition metals with those of the second and third series metals in the respective vertical columns. Give special emphasis on the following points:
electronic configurations
Electronic Configurations: The first transition series (3d) elements have general electronic configuration [Ar] 3d¹⁻¹⁰ 4s¹⁻². The second series (4d) have [Kr] 4d¹⁻¹⁰ 5s⁰⁻² and third series (5d) have [Xe] 4f¹⁴ 5d¹⁻¹⁰ 6s⁰⁻². Irregularities in electronic configurations are more common in second and third series due to intervention of f-orbitals.
oxidation states
Oxidation States: The first series elements show variable oxidation states. The second and third series elements exhibit higher oxidation states more frequently. The stability of higher oxidation states increases down the group in second and third series compared to first series.
ionisation enthalpies and
Ionisation Enthalpies: The ionisation enthalpies generally increase from first to second series. However, due to lanthanide contraction, the ionisation enthalpies of second and third series elements become comparable. The poor shielding effect of d-electrons affects the values.
atomic sizes.
Atomic Sizes: Atomic size increases from first to second series. However, due to lanthanide contraction, the atomic sizes of second and third series elements in the same vertical column are nearly the same. This results in greater similarities between second and third series elements.
Explanation
This question from NCERT Chapter 4 (The d-Block and f-Block Elements) asks students to compare the three transition series vertically. The key concept is the lanthanide contraction which makes second and third series elements similar in properties. Students should mention that while properties change from first to second series, the third series resembles the second due to similar atomic radii caused by lanthanide contraction.