Question

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

Answer 1

Answer:

Explanation:

it becomes easy to remove electron from outermost orbital for bigger atoms, due to less effective nuclear charge. Thus ionisation energy is less for 7th period elements than 6th period elements. That is why ​Ce, Pr and Nd have higher ionisation energy than Th, Pa and U

Answer 2

Answer

Explanation:

All these elements lie in inner transition metal block. Ce, Pr and Nd lie in 6th period and Th, Pa and U lie in 7th period. As we move down the group, the size increases as the shell increases. So, it becomes easy to remove electron from outermost orbital for bigger atoms, due to less effective nuclear charge. Thus ionisation energy is less for 7th period elements than 6th period elements. That is why ​Ce,  Pr  and Nd have higher ionisation energy than Th, Pa and U.