question_answer

Out of H and \[{{H}_{2}},\] the latter has higher first ionization energy while out of \[O\] and \[{{O}_{2}},\] the former has higher first ionization energy. Explain why.

Answer:

                In \[{{H}_{2}},\] first electron has to be removed from \[\sigma (1s)\] which has lower energy (more stable) than H-atom. In \[{{O}_{2}},\] first electron has to be removed from \[{{\pi }^{*}}\,(2{{p}_{x}})\,or\,{{\pi }^{*}}\,(2{{p}_{y}})\] orbital which has higher energy than 2 p-orbital of O-atom.