Ionization energy, what's needed to remove 1 electron from 1 atom, is high for this non-reactive 6-element group
The 
energy required to remove one valence electron is the first ionization .... As you 
go up a group, the ionization energy increases, because there are... [DOC] [TLE] Ionization Energies - Chemistry LibreTexts [PAR] Sep 28, 2015 ... All elements have a first ionization energy - even atoms which do not form ...