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Hunds rules empirical observavons for the electron

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Unformatted text preview: riodic! Periodic table Carbon… •  Last Vme we were looking at the electronic configuraVon of carbon and we bumped into a problem… 2p 2s What do we do here? Spin up or down? ? Answer this next Vme… 1s • Could equally well put it spin up or down, but which is the ground state? Hund’s rules •  Empirical observaVons for the electron configuraVons of the ground states of mulV ­electron atoms Hund’s Rules: •  Maximize S (spin) •  Once S is maximized, maximize L •  For half ­filled or less, the lowest J=L+S is the lowest E •  For more than half ­filled, the highest J is the lowest E Carbon… •  So now we know where to put that last electron… 2p 2s What do we do here? Hund’s first rule: SPIN UP Maximizes S as S=1 rather than S=0 1s Molecules •  Stable arrangements of atoms •  Must consider now the nuclear degree of freedom (although much slower than electrons) •  Strategy: –  Calculate the electronic moVon based on staVc nucleus –  Calculate the nuclear moVon considering the electrons are smeared out charge distribuVon. •  Mass of nucleus = mass of proton = 2000 Vmes that of electron Simplest molecule: H2+ + r + R •  Protons close together: r + + = r ER!0 = "13.6 Z 2 = "54.4 eV +2 Looks like a singly ionized He atom… •  Protons far apart: + r + Looks like a H atom… E0 = !13.6 eV Energy vs nuclear distance proton contribuVon e2 4!!0 R R...
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