Question

Explain why the ionisation energy of boron is less than that of $Be$?

Answer 1

Ionization enthalpy increases as we from left to right in a period.

But $Be$ shows higher ionization enthalpy than $B$.

This is because of the completely filled electronic configuration of the $Be$ whereas the boron has incompletely filled p subshell.

$Be:1s^{2}2s^2$

$B:1s^{2}2s^{2}2p^1$

It is difficult to remove an electron from completely filled subshells than incompletely filled one.