# How would you determine which of these elements has the highest first ionization energy?

Jul 2, 2016

We have the Noble Gases listed in their Periodic Order. The highest first ionization energy is undoubtedly that of $H e$. Why? Because $H e$ is the smallest atom, and because helium has the greatest effective nuclear charge. Given what I have said, you should be able to determine the order of ionization energies:
${\text{Gas"+Deltararr"Gas}}^{+} + {e}^{-}$