Question

Answer the following

Explain trends in ionisation enthalpies of d-block elements.

Answer 1

1. The ionization enthalpies of transition elements are intermediate between those of s-block or p-block elements. This suggests that transition elements are less electropositive than elements of groups 1 and 2.
2. As the atomic number increases across a transition series, the first ionization energy increases with some irregularities.
3. Ionization enthalpies for a given element increases from the first ionization enthalpy, IE₁ to the third ionization enthalpy, IE₃.
4. The atoms of elements of the third transition series possess filled 4f-orbitals. 4f orbitals show a poor shielding effect on account of their peculiar diffused shape. As a result, the valence electrons experience a greater nuclear attraction. A greater amount of energy is required to ionize elements of the third transition series. The ionization enthalpies of the elements of the third transition series are, therefore much higher than the first and second series.