The trend for ionization energy is a general increase from left to right across a period. However, beryllium (Be) is found to have a higher first ionization energy value than boron (B). Explain this exception to the general trend in terms of electron arrangements and attraction/repulsion.
PLEASE HELP!!!!!

Question

The trend for ionization energy is a general increase from left to right across a period. However, beryllium (Be) is found to have a higher first ionization energy value than boron (B). Explain this exception to the general trend in terms of electron arrangements and attraction/repulsion.
PLEASE HELP!!!!!

anonymous · Answer

WILL GIVE MEDAL!

aaronq · Answer

it has to do with the orbitals in which these electrons reside.

Be is $1s^22s^2$ 
B is $1s^22s^22p^1$

The lone electron on the p orbital of B is easier to remove, one of the reasons for this is due to the "shielding" effect of positive charge by the $s$ electrons on the $p$ electrons. The result is that the p electron experiences less attraction to the nucleus and hence it takes less energy to ionize.