Whats coming up??? Oct 25The atmosphere, part 1Ch. 8 Oct 27Midterm No lecture Oct 29The atmosphere, part 2Ch. 8 Nov 1Light, blackbodies, BohrCh. 9 Nov 3,5Postulates of QM, p-in-a-boxCh. 9 Nov 8,10Hydrogen and multi e atoms Ch. 9 Nov 12Multi-electron atomsCh.9,10 Nov 15Periodic propertiesCh. 10 Nov 17Periodic propertiesCh. 10 Nov 19Valence-bond; Lewis structures Ch. 11 Nov 22VSEPRCh. 11 Nov 24Hybrid orbitals; VSEPRCh. 11, 12 Nov 26Hybrid orbitals; MO theoryCh. 12 Nov 29MO theoryCh. 12 Dec 1bonding wrapupCh. 11,12 Dec 2Review for exam The Final Exam December 13 (Monday) 9:00 12:00 Cumulative (covers everything!!) Worth 50% of total mark Multiple choice The Final Exam From my portion, you are responsible for: Chapter 8 material from my lecture notes Chapter 9 everything Chapter 10 everything Chapter 11 everything Chapter 12 everything except 12.7 The Final Exam You will need to remember Relationship between photon energy and frequency / wavelength De Broglie AND Heisenberg relationships Equations for energies of a particle-in-a-box AND of the hydrogen atom VSEPR shapes AND hybribizations which give them My office hours next week Wednesday Dec 8: AND 2-4 Friday Dec 10: AND 2-4 THE MOs FORMED BY TWO 1s ORBITALS The molecular orbitals. E Expected orbital splitting: 2s2s 2s*2s* 2s2s 2s2s 2p2p 2p*2p* 2p2p 2p2p 2p2p 2p*2p* The do not split as much because of weaker overlap. But the s and p along the internuclear axis DO interact This pushes the 2p up.. Why does this happen? pure s and p orbitals O 2 F 2 Ne 2 pure s-p hybrids B 2 C 2 N 2 -type orbitals have different energies depending on s-p interactions 2p orbitals 2p 2s Increasing s-p interaction E MODIFIED ENERGY LEVEL DIAGRAM 2s2s 2s*2s* 2s2s 2s2s 2p2p 2p*2p* 2p2p 2p2p 2p2p 2p*2p* interaction 2p * 2p * 2p or 2p 2p or 2p 2s * 2s Magnetism Bond order Bond E. (kJ/mol) Bond length(pm) Second row diatomic molecules B 2 Para C 2 Dia N 2 Dia O 2 Para F 2 Dia E NOTE SWITCH OF LABELS 2s2s 2s*2s* 2s2s 2s2s E 2p2p 2p*2p* 2p2p 2p2p 2p2p 2p*2p* 2s2s 2s*2s* 2s2s 2s2s 2p*2p* 2p2p 2p2p 2p2p 2p*2p* 2p2p HETERONUCLEAR DIATOMICS Energies of 1s and 2p orbitals are very different E = R H Z eff 2 / n 2 Electronegativities! Outcomes of MO Model As bond order increases, bond energy increases and bond length decreases. Bond order is not absolutely associated with a particular bond energy. N 2 has a triple bond, and a correspondingly high bond energy. O 2 is paramagnetic. This is predicted by the MO model, not by the LE model, which predicts diamagnetism. Putting our bonding models together The VSEPR / hybridization approach is good at explaining shapes around a central atom in a molecule BUT, since it depends on keeping electrons in pairs at all times, it is not so good at predicting electron distributions (like in oxygen!) Is there a way to bring them together? Lets go back to RESONANCE The Resonance Structures for O 3 and NO 3 - Double bonds involve interacting p orbitals, outside of the bonding line p- bonding spread over whole molecule p- antibonding p- non-bonding We can make a similar molecular orbital for the nitrate ion too! Benzene - aromatic molecules Figure 9.48 The Pi System for Benzene Combining our 2 Models bonds can be described as being localized. bonding must be treated as being delocalized.