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S a or a s which has a lower energy r as r 0 r s a s

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Unformatted text preview: 0 R  ­13.6  ­54.4 electron contribuVon There is an equilibrium point R0~0.106 nm at an energy of 2.8 eV below  ­13.6 eV. Where is the electron? The Hamiltonian for the system is: (remember the nuclei are considered staVonary) 2 # pe e2 e2 e2 & ! ! + % () (r, R ) = E) (r, R ) $ 2 me 4"!0 r1 4"!0 r2 4"!0 R ' ? + + R p ­p repulsion raises energy + ✓ + R electron screens the nuclear charge i.e. it’s SHARED between the two Valence bonds •  Consider H2 molecule: Two unfilled 1s shells •  Total wavefuncVon! must be anVsymmetric under exchange •  Can either have ! S ! A or ! A "S which has a lower energy? R As R ! 0 R !S !A !S !A approaches ground state wavefuncVon approaches 1st excited state wavefuncVon i.e. ground state wavefuncVon is that of the spin singlet electrons shared between the nuclei. Ionic bonding •  Consider NaCl (table salt) •  Na atom: 1s22s22p6 + 3s and the Cl atom 1s22s22p63s2 + 3p5 core core outer shell outer shell Na wants to give up an electron, Cl wants to accept an electron. How much energy does this cost to do? Cost of energy to remove the 1 electron from Na: 5.1 eV Energy released by Cl when it receives 1 electron to close its shell: 3.8 eV So total cost in energy is 1.3 eV…..which is sVll >> room temperature. Ionic bonding Are you sure we can be together? Cl ­ Yes, I’m posiVve Na+ Once Cl accepts Na’s...
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