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What’s coming up???

What’s coming up???. Oct 25 The atmosphere, part 1 Ch. 8 Oct 27 Midterm … No lecture Oct 29 The atmosphere, part 2 Ch. 8 Nov 1 Light, blackbodies, Bohr Ch. 9 Nov 3,5 Postulates of QM, p-in-a-box Ch. 9 Nov 8,10 Hydrogen and multi – e atoms Ch. 9 Nov 12 Multi-electron atoms Ch.9,10

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What’s coming up???

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  1. What’s coming up??? • Oct 25 The atmosphere, part 1 Ch. 8 • Oct 27 Midterm … No lecture • Oct 29 The atmosphere, part 2 Ch. 8 • Nov 1 Light, blackbodies, Bohr Ch. 9 • Nov 3,5 Postulates of QM, p-in-a-box Ch. 9 • Nov 8,10 Hydrogen and multi – e atoms Ch. 9 • Nov 12 Multi-electron atoms Ch.9,10 • Nov 15 Periodic properties Ch. 10 • Nov 17 Periodic properties Ch. 10 • Nov 19 Valence-bond; Lewis structures Ch. 11 • Nov 22 VSEPR Ch. 11 • Nov 24 Hybrid orbitals; VSEPR Ch. 11, 12 • Nov 26 Hybrid orbitals; MO theory Ch. 12 • Nov 29 MO theory Ch. 12 • Dec 1 bonding wrapup Ch. 11,12 • Dec 2 Review for exam

  2. Describing the bonding in more complicated molecules…... PROPYNE: CH3CCH 16 valence electrons Lewis Dot Structure….. H H C H C C H CENTRAL CARBON NEEDS OCTET

  3. sp sp3 PROPYNE: CH3CCH has the structure H C C C H H H Linear Carbons Tetrahedral Carbon: Hybridization? Hybridization?

  4. C p overlaps with C p p bonds C sp3 overlaps with H 1s C sp overlaps with C sp s bond s bond s bond C sp3 overlaps with C sp PROPYNE: CH3CCH has the bonding H H C C C H H

  5. H These four atoms are in a straight line C C C FREE ROTATION of Methyl Group. H H H

  6. LACTIC ACID O H H H C C C H O O H H The bondingframe work of lactic acid

  7. QUESTION O H H H C C C H O O H H THE BOND ANGLE SHOWN IS 1 120° 2 90° 3 180° 4 109°

  8. QUESTION O H H H C C C H O O H H THE BOND ANGLE SHOWN IS 1 120° 2 90° 3 180° 4 109°

  9. QUESTION O H H H C C C H O O H H THE BOND ANGLE SHOWN IS 1 109° 2 90° 3 120° 4 180°

  10. LACTIC ACID O O H H C H O C C H H H

  11. OK, so we have it all figured out! … or do we?? Let’s think about oxygen, O2 12 electrons … Lewis picture gives :O::O: .. .. 3 electron groups around each … sp2 and 1200

  12. s bond p bond O O All electrons paired … diamagnetic BUT O2 is paramagnetic unpaired electrons!!

  13. 1s 2s 2p N 1s22s22p3 MAGNETIC PROPERTIES Atoms, molecules or ions with at least one unpaired electron are paramagnetic. Paramagnetic materials are strongly attracted to magnetic fields. Nitrogen atom is PARAMAGNETIC

  14. Let’s try another approach …

  15. Combining the two 1S orbitals from two hydrogen atoms will give another way to think about bonding

  16. COMBINATION OF ORBITALS Remember, when we take linear combinations of orbitals we get out as many as we put in. Here, the sum of the 2 orbitals 1sA + 1sB = MO1 builds up electron density between nuclei. 90% probability

  17. COMBINATION OF ORBITALS 1sA – 1sB = MO2 results in low electron density between nuclei 1sA + 1sB = MO1 builds up electron density between nuclei.

  18. THE MO’s FORMED BY TWO 1s ORBITALS

  19. ANTI-BONDING s1s* 1sA – 1sB = MO2 BONDING s1s Each orbital can hold up to two electrons. 1sA + 1sB = MO1

  20. COMBINING TWO 1s ORBITALS Energy of a 1s orbital in a free atom Energy of a 1s orbital in a free atom A B E

  21. COMBINING TWO 1s ORBITALS Energy of a 1s orbital in a free atom Energy of a 1s orbital in a free atom A B E s1s Energy of 1sA+1sB MO ADDITION gives an Energy more negative than average of original orbitals

  22. SUBTRACTION gives an…. Energy more positive than average of original orbitals s1s* Energy of a 1s orbital in a free atom Energy of a 1s orbital in a free atom A B E s1s ADDITION gives an…. Energy more negative than average of original orbitals

  23. COMBINING TWO 1s ORBITALS s1s* A B 1sB 1sA E s1s

  24. The bonding in H2 H H2 H s1s* E 1s 1s s1s

  25. H H2 H s1s* E 1s 1s s1s H2: (s1s)2

  26. He2 1s2 Atomic configuration of He He He2 He s1s* E 1s 1s s1s One pair of electrons goes in s1s and the next pair ins1s*

  27. He2: (s1s)2(s1s*)2 The He2 molecule is not a stable species. He He2 He s1s* E 1s 1s s1s The bonding effect of the (s1s)2 is cancelled by the antibonding effect of (s1s*)2

  28. BOND ORDER Useful concept: The net number of bonds existing after the cancellation of bonds by antibonds. the electronic configuration is…. In He2 (s1s)2(s1s*)2 the two bonding electrons were cancelled out by the two antibonding electrons. There is no BOND! BOND ORDER = 0

  29. BOND ORDER A measure of bond strength and molecular stability. If # of bonding electrons > # of antibonding electrons the molecule is predicted to be stable { Bond order } # of bonding electrons(nb) = # of antibonding electrons (na) 1/2 – = (nb - na) 1/2 A high bond order indicates high bond energy and short bond length. Consider H2+,H2,He2+,He2……….

  30. First row diatomic molecules and ions s1s* s1s Magnetism Bond order Bond energy (kJ/mol) Bond length (pm) H2 Dia- 1 436 74 H2+ Para- ½ 225 106 He2+ Para- ½ 251 108 He2 — 0 — — E

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