Question

Why ionisation enthalpy of lanthanides is higher than actinides

Answer 1

Answer:

in lanthanides electrons enter in the 4f orbital but in actinides it is in 5f orbital .

the 5f orbitals extrude outside more than 4f. So 4f electrons are more influenced by nuclear attraction than 5f electrons. So removing electron from 4f is harder that reflects the ionisation energy trend.

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