1.

Ionisation enthalpies of Ce, Pr and Nd are higher than those of Th, Pa and U. why ?

Answer» The first three element belong to lanthanoids (4f-obitals are filled ) while the last three elements ar actinoids (5f orbital are filled ). We all know that 5f orbitals have less penetration in the innner core as compared to 4f orbitals. As a result, ionisation enthalpies of lanthanoids are expected to be more than those of actinoids.


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