# What is ionization energy trend?

As a physical scientist you should seek out the data. As nuclear charge, $Z$, increases, the nucleus has greater electrostatic attraction for the valence electrons. The result is that (i) atomic radii decrease, and (ii) ionization enthalpies increase ACROSS the Period from left to right.
Down a Group, the valence electron is further removed from the nuclear charge, and inner electrons tend to shield $Z$. Ionization energies thus decrease.