Arrange the second period elements in the increasing order of their first ionization enthalpies. Explain why Be has higher `IE_(1)` then B.

Explanation

`Li < B < Be < C < O < N < F`
In Be the electron to be removed is from 2s orbital whereas in B the electron to be removed is from 2p. The penetration of a 2s electron to the nucleus is more than that of 2p electron, thus 2s electron is strongly attractd by the nucleus then 2p electron. The 2s electron is shielded by only one orbital 1s in Be but 2p electron is shielded by two orbitals 1s and 2s. So the `IE_(1)` of Be is more than `IE_(1)` of `B`.