Rank these elements according to first ionization energy. Highest ionization energy Kr Br Se As Ge Ga Ca K Lowest ionization energy Incorrect. You have correctly identified the general trend, with the noble gas at the top and the alkali metal at the bottom. However, there are two exceptions within this general trend. The atom with the ns electron configuration is particularly stable and should move up one spot in the ranking. Similarly, the atom with the nsnp electron configuration is particularly stable and should move up one spot in the ranking.