Lecture36.pptx

Consistent with the pauli principle the state with

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Unformatted text preview: Closed ­shell” configuraBons are always 1S0. 5 6 For helium: L=0, S=0, J=0, so: 2 S +1 LJ = 1S0 1 4/15/11 Now, add two more elements: Z 1 2 3 4 5 6 Element H He Li Be B C configura0on (1s) (1s)2 (1s)2(2s) (1s)2(2s)2 (He)(2s)2(2p) (He)(2s)2(2p)2 2S+1L J 2S 1/2 0 Hund’s Rules: 1.  Consistent with the Pauli Principle, the state with the highest total spin S will have the lowest energy. 2.  For a given S, the state with the highest total orbital angular momentum L (consistent with anBsymmetrizaBon) will have the lowest energy. 3.  If a subshell (n,l) is no more than half full, then J=|L ­S|. Otherwise it is J=|L+S|. There are some physical plausibility arguments behind these “rules.” (Spin ­orbit coupling, electron ­electron interacBons, etc…) Back to boron: Rule #3 says J=1/2 (and not J=3/2). 7 8 1S 2S 1/2 0 1S 2P ??? ??? Boron looks easy. Start with a closed ­shel...
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