I heard someone mentioned that Hund's rules do not always work.

Looking at atomic spectrum: (https://qudev.phys.ethz.ch/phys4/PHYS4_lecture10v1_2page.pdf page 10 Hg spectrum) How could singlet (with multiplicity 1) has lower energy than triplet (with multiplicity 3)?

When will hunds' fail and how do we work with them?

  • $\begingroup$ I think you might be mis-understanding the Hg atom. In the ground state the 6s and 5d levels are full, so all orbitals are doubly occupied and it is a singlet. The next level up is the 6p. So when the atom is excited there will be two unpaired electrons when one enters 6p, so the state will be a triplet. $\endgroup$ – Paul Young Feb 20 '19 at 16:34
  • $\begingroup$ Try asking a similar question about platinum :-o $\endgroup$ – Paul Young Feb 20 '19 at 16:40

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