1. Chapter 8 Second set of Chapt. 8 homework dates extended until after break Lab Notes Today’s Topic: Electron Distribution in Molecules (8.5) Molecular Shape (8.6) Molecular Polarity (8.7) November 20, 2009

4. Formal Charge and Oxidation Number Examples

5. Partial Charges

6. Charges Within Molecules Formal charge  Electrons are shared evenly throughout molecule  Closer to “real” charge than oxidation number  Use to determine which nonequivalent resonance structure is more likely Oxidation Number  Bonding electrons “belong” to more electronegative atom  Quick and easy to determine without Lewis structure  Doesn’t really reflect actual charges on atoms  Use to determine whether compounds are oxidized/reduced in chemical reactions Partial Charges  How electrons are really distributed in a molecule  Need computer to calculate  Used only when you need very accurate description- molecular modeling

7. What is the formal charge on C in CN - ? 1. -2 2. -1 3. 0 4. +1 5. +2

8. What is the formal charge on C in CN - ? 1. -2 2. -1 3. 0 4. +1 5. +2

9. Molecular Structure Chemical Formula Lewis Structure #Structural Pairs (Valence e - Pairs) Electron Pair Geometry Molecular Geometry

10. Lewis # Structural Electron Molecular Structure Pairs Geometry Geometry # Structural Pairs = # bonded + # lone on central atom atoms pairs

11. # Structural Pairs determines Electron Pair Geometry

14. What is the electron pair geometry of ozone? 1. Linear 2. Trigonal planar 3. Tetrahedral 4. Trigonal bipyramidal 5. octahedral

15. What is the electron pair geometry of SCN - ? 1. Linear 2. Trigonal planar 3. Tetrahedral 4. Trigonal bipyramidal 5. octahedral

16. Molecular Geometry = Electron Pair Geometry, ignoring lone pairs BF 3 and O 3

17. Molecular Geometry = Electron Pair Geometry, ignoring lone pairs

18. Lone pairs always go in equatorial sites Molecular Geometry = Electron Pair Geometry, ignoring lone pairs

20. What is the molecular geometry of NO 2 - ? 1. Linear 2. Bent 3. Trigonal planar 4. Tetrahedral 5. Trigonal pyramid 6. T-shaped 7. Square pyramid 8. Square planar 9. octahedral

21. What is the molecular geometry of … 1. Linear 2. Bent 3. Trigonal planar 4. Tetrahedral 5. Trigonal pyramid 6. T-shaped 7. Square pyramid 8. Square planar 9. octahedral

22. What is the molecular geometry of … 1. Linear 2. Bent 3. Trigonal planar 4. Tetrahedral 5. Trigonal pyramid 6. T-shaped 7. Square pyramid 8. Square planar 9. octahedral