Which of the following best describes the relationship between 1st ionization energy and atomic radius?

             The relationship between 1st ionization energy and atomic radius is inversely proportional.

                           Ionization Energy is defined as, "the minimum amount of energy required to remove the valence electron from the valence shell of an atom in its gaseous state".

Atomic Radius Greater:

                                      Greater atomic radius means greater distance between the valence electron and nucleus hence, electron will experience less nuclear attraction and therefore, is easily removed.

Atomic Radius Smaller:

                                       Smaller atomic radius means less distance between valence electron and nucleus hence, more nuclear charge is experienced by valence electron therefore, more strongly attracted by nucleus and requires more energy to ne knocked out.