Question
Explain trends in ionisation enthalpies of d-block elements.
✓
Answer
- The ionisation enthalpies of transition elements are quite high and lie between those of $5$-block and p-block elements. This is because the nuclear charge and atomic radii of transition elements lie between those of $5$-block and p-block elements.
- As atomic number of transition elements increases along the period and along the group, first ionisation enthalpy increases even though the increase is not regular.
- If $IE_{1;} IE_2$ and $IE_3$ are the first, second and third ionisation enthalpies of the transition elements, then $IE_1 < IE_2 < IE_3.$
- In the transition elements, the added last differentiating electron enters into $(n – 1)$ d-orbital and shields the valence electrons from the nuclear attraction. This gives rise to the screening effect of $(n – 1)$ d-electrons.
- Due to this screening effect of $(n – 1)$ d electrons, the ionisation enthalpy increases slowly and the increase is not very regular.
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