Question

First ionization energy of boron is less than Be but size of Be is more than boron. Why?

Answer 1

Electronic configuration of ₄Ве = 2, 2 = 1s² , 2s²

Electronic configuration of ₅B = 2, 3 = 1s² , 2s² , 2p¹

In case of Be, more energy is required to remove an electron from 2s orbital as it is completely filled as compared to B. So, first I.E. of boron is less than Be. But size of Be is more than boron because atomic size decreases from left to right in a period due to increase in nuclear charge.