What periodic trends exist for ionization energy?

1 Answer
Nov 24, 2015

Reasonably, ionization energies should increase across a Period, and decrease down a Group.


Simple electrostatics should be your guide. Going from left to right, nuclear charges increase sequentially, while electrons are added to the same shell. Nuclear charge wins, and ionization energies increase.

Going down a Group, inner shell electrons can effectively shield the outer electrons from nuclear charge. Shielding wins, and ionization energies decrease.

You will find a few anomalies, but the same pattern exists for atomic size (i.e. atomic size decreases across the period).

As a physical scientist, you should approach the problem quantitatively. Search out ionization energy trends versus atomic number on the web, and find a diagram.