Why there is a change in sequence of energies for O2, F2, Ne2 in molecular orbital theory?

Dear Student,

The molecular orbital energy level for O2,Fe2,Ne2 are as shown below,

The configurations for these molecules are the same for the two schemes (except for reversal of the inner s2p and p2p levels) and thus would not predict differing numbers of unpaired electrons. ‚ÄčIn O2, F2, Ne2 the larger Z (nuclear charge) makes the energy of the 2s atomic orbital much lower than the 2p atomic orbital and thus the 2s and 2p on these’ DO NOT mix when forming m.o.’s. ‚ÄčThus there will be of no significant difference in energy change.


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