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Take out CLICKERS : “GO 41 GO” -or- “CH 41 CH” and CALCULATORS NEXT LECTURE: Friday, Nov. 13; Bring CLICKERS READ

Chemistry 177 November 11, 2009. Take out CLICKERS : “GO 41 GO” -or- “CH 41 CH” and CALCULATORS NEXT LECTURE: Friday, Nov. 13; Bring CLICKERS READ BLBM, Chapters 8 and 9 HOMEWORK #12: Ch. 8: # 62, 66, 90, 92; Due in Recitation,

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Take out CLICKERS : “GO 41 GO” -or- “CH 41 CH” and CALCULATORS NEXT LECTURE: Friday, Nov. 13; Bring CLICKERS READ

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  1. Chemistry 177 November 11, 2009 Take out CLICKERS: “GO 41 GO” -or- “CH 41 CH” and CALCULATORS NEXT LECTURE:Friday, Nov. 13; Bring CLICKERS READ BLBM,Chapters 8 and 9 HOMEWORK #12: Ch. 8: # 62, 66, 90, 92; Due in Recitation, #13:Ch. 9: # 22, 26, 36, 56 Thursday, Nov. 12 DCI #10: P. 135, # 4, 5, 6 (Molecular Structure) HOUR EXAM #4: Monday, November 16, 6:30-7:30 PM Q&A SESSIONS: Sunday, November 15, 7:00 PM 1414 Molecular Biology & 1002 Gilman OPTIONAL EXAM: Monday, December 7, 6:30-7:30 PM (Multiple Choice) FINAL EXAM: Monday, December 14, 7-9 PM

  2. Chapter 8: Basic Concepts of Chemical Bonding Molecular Geometry:Lewis Structures (Violating the Octet Rule) Phosphorus Pentafluoride: PF5 F 5 BOND PAIRS F “Hypervalent” Molecules P violates the octet rule by being surrounded by more than 8 valence electrons (4 electron pairs). F P F 15 LONE PAIRS F 5 + 5(7) = 40 e (20 e pairs) Formal Charges: P: 5  (0 + 51) = 0 F: 7  (32 + 11) = 0

  3. CO2: 5 DOMAINS PF5: 2 DOMAINS BF3: 3 DOMAINS SF6: 6 DOMAINS 4 DOMAINS NH3: Chapter 9: Molecular Geometry and Bonding Theories Molecular Shapes: VSEPR + Lewis Structures Valence Shell Electron Pair Repulsion: What are the shapes of molecules? Determine the local structure at an atom in a molecule or solid; Count the regions of electron-pairs around an atom: Single bonds, Lone Pairs, Multiple Bonds (Single Domain) Examples: (Use Lewis Structures)

  4. Chapter 9: Molecular Geometry and Bonding Theories Molecular Shapes: VSEPR + Lewis Structures

  5. 4 BOND Pairs/1 LONE Pair OR AXIAL Ligands 90 EQUATORIAL Ligands 120 164.6 pm 154.5 pm Feq-S-Feq = 101.6 Fax-S-Feq < 90 Fax-S-Fax = 173.1 S-Feq = 154.5 pm; S-Fax = 164.6 pm Fax-Cl-Feq = 87.5 Fax-Cl-Fax = 175 Cl-Feq = 159.8 pm; Cl-Fax = 169.8 pm Chapter 9: Molecular Geometry and Bonding Theories Molecular Shapes: VSEPR (Trigonal Bipyramid) 157.7 pm 153.4 pm Feq-P-Feq = 120 Fax-P-Feq = 90 Fax-P-Fax = 180 P-Feq = 153.4 pm; P-Fax = 157.7 pm

  6. Chapter 9: Molecular Geometry and Bonding Theories Molecular Shapes: VSEPR + Lewis Structures

  7. 4 BOND Pairs/2 LONE Pairs 5 BOND Pairs/1 LONE Pair Fax-Br-Feq = 84 Br-Feq = 180 pm; Br-Fax = 168 pm Chapter 9: Molecular Geometry and Bonding Theories Molecular Shapes: VSEPR (Octahedron)

  8. Chapter 8: Basic Concepts of Chemical Bonding Molecular Geometry:Lewis Structures (Violating the Octet Rule) Hypovalent Molecules Hypervalent Molecules OCTET RULE

  9. CH4(g)  H(g) + CH3(g); DH0 = D(HCH3) = 427 kJ/mol CH4(g)  C(g) + 4 H(g); DH0 = 1660 kJ/mol = 4 (415 kJ/mol) D(CH) = 413 kJ/mol AVERAGE over many molecules Chapter 8: Basic Concepts of Chemical Bonding Bond Enthalpies = Bond Dissociation Energies DH0 for reactions involving molecular species can be well estimated using average bond enthalpies for chemical bonds in the molecules… Bond Enthalpy = Enthalpy change (in kJ) to homolytically break a (polar) covalent bond (Tabulated…) Cl2(g)  2Cl(g); DH0 = D(ClCl) = 242 kJ/mol (bonds) HCl(g)  H(g) + Cl(g); DH0 = D(HCl) = 431 kJ/mol

  10. Chapter 8: Basic Concepts of Chemical Bonding Bond Enthalpies DH0 REACTANTS PRODUCTS N2(g) + 3 H2(g)  2 NH3(g) (1) (2) REACTANTS GASEOUS ATOMS  PRODUCTS

  11. HCCH HOH O=O O=C=O 413 kJ 839 kJ 495 kJ 799 kJ 463 kJ Chapter 8: Basic Concepts of Chemical Bonding Bond Enthalpies Example: Use average bond enthalpies to estimate the enthalpy of combustion of acetylene gas, C2H2(g). 2 C2H2(g) + 5 O2(g)  4 CO2(g) + 2 H2O(g) DH0= 2511 kJ

  12. Chapter 8: Basic Concepts of Chemical Bonding Molecular Geometry:Lewis Structures (Violating the Octet Rule) Nitrogen Dioxide: NO2 O N O O N O

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