Honors Chemistry

1. Honors Chemistry Chapter 10: Chemical Bonding II

2. 10.1 Molecular Geometry • Study of the shapes of molecules • Molecule’s geometry affects properties • Valence shell • outermost occupied shell • Holds electrons involved in bonding • VSEPR Model • Valence Shell Electron Pair Repulsion • Accounts for arrangement of electron pairs around a central atom in terms of electrostatic repulsion

3. 10.1 Molecular Geometry • AXnEm • Draw Lewis Structure • Identify central atom (A) • Count electron pairs • X = bonding pairs • E = lone pairs

4. linear tetrahedral trigonal planar trigonal bipyramidal octahedral Electron-group repulsions and the five basic molecular shapes.

5. 10.1 Molecular Geometry

6. 10.1 Molecular Geometry

7. 10.1 Molecular Geometry

8. 10.1 Molecular Geometry

9. 10.1 Molecular Geometry

10. 10.1 Molecular Geometry

11. 10.1 Molecular Geometry • True bond angles deviate from ideal • Lone pairs are more repulsive than bonding pairs • Triple bonds > double bonds > single bonds in terms of repulsion • Molecules with multiple centers • Apply VSEPR to each central atom

12. 10.1 Molecular Geometry • Find the shapes and bond angles: • AsH3 • CS2 • OF2 • NO3- • AlCl4- • I3- • C2H4

13. 10.2 Dipole Moments • Vector describing the polarity of the entire molecule • Symbol for dipole moment is m • Measured in Debyes • Depends on bond polarity and geometry • Examples: O2, CO2, H2O, CH4, CCl4, NH3 • Larger molecules become more complex • cis-dichloroethylene,trans-dichloroethylene

14. 10.3 Valence Bond Theory • More complete theory of bonding • Based on Quantum Mechanics • Explains bond energies and bond lengths • Consider overlap of 1s orbitals as two H atoms approach each other • Nucleus-electron attraction forces • Nucleus-nucleus repulsion forces

15. 10.3 Valence Bond Theory

16. 10.4 Hybridization • Consider compound of C and H • Carbon has 2s2 sp2 configuration • Basic QM would predict • CH2 • 90o bond angles • Actual compound is CH4, 109.5o angles • Need to merge s and p orbitals into a new set of atomic orbitals (hybrids)

17. The sp3 hybrid orbitals in CH4.

18. The sp3 hybrid orbitals in NH3.

19. The sp3 hybrid orbitals in H2O.

20. The sp2 hybrid orbitals in BF3.

21. The sp hybrid orbitals in gaseous BeCl2.

22. 10.4 Hybridization

23. 10.4 Hybridization • Procedure for hybridizing atomic orbitals: • 1. Draw Lewis structure • 2. Use VSEPR to predict the overall geometry of the electron pairs • 3. Deduce the hybridization of the central atom from the geometry

24. 10.5 Double and Triple Bonds • sp2 and sp hybrids don’t use all p orbitals • “Leftover” p’s can overlap to form bonds • Sigma bond (s) • Overlap of s or head-on p orbitals • e- density between nuclei • Pi bond (p) • Sideways overlap of p orbitals • e- density above and below nuclei

25. both C are sp3 hybridized s-sp3 overlaps to s bonds sp3-sp3 overlap to form a s bond relatively even distribution of electron density over all s bonds The s bonds in ethane(C2H6).

26. overlap in one position - s p overlap -  electron density The s and p bonds in ethylene (C2H4).

27. overlap in one position - s p overlap -  The s and p bonds in acetylene (C2H2).

28. 10.5 Double and Triple Bonds Electron density and bond order.

29. CIS TRANS 10.5 Double and Triple Bonds Restricted rotation of p-bonded molecules in C2H2Cl2.

30. 10.6 Molecular Orbital Theory • VB allows e- to stay in atomic orbitals • This is only an approximation • Fails to account for some properties of molecules (eg, magnetism) • Reality – orbitals are delocalized across the entire molecule • Molecular Orbital Theory – based on QM • Rebuild y for the entire molecule

31. Amplitudes of wave functions subtracted. An analogy between light waves and atomic wave functions. Amplitudes of wave functions added

32. Contours and energies of the bonding and antibonding molecular orbitals (MOs) in H2. The bonding MO is lower in energy and the antibonding MO is higher in energy than the AOs that combined to form them.

33. 1s 1s AO of H AO of H The MO diagram for H2. Filling molecular orbitals with electrons follows the same concept as filling atomic orbitals. s*1s Energy H2 bond order = 1/2(2-0) = 1 s1s MO of H2

34. s*1s Energy 1s 1s 1s 1s s1s AO of He AO of He+ AO of He AO of He MO diagram for He2+ and He2. s*1s Energy s1s MO of He+ MO of He2 He2 bond order = 0 He2+ bond order = 1/2

35. s*2s s*2s 2s 2s 2s 2s s2s s2s Bonding in s-block homonuclear diatomic molecules. Be2 Li2 Be2 bond order = 0 Li2 bond order = 1

36. Contours and energies of s and p MOs through combinations of 2p atomic orbitals.

37. Relative MO energy levels for Period 2 homonuclear diatomic molecules. without 2s-2p mixing with 2s-2p mixing MO energy levels for O2, F2, and Ne2 MO energy levels for B2, C2, and N2

38. MO occupancy and molecular properties for B2 through Ne2

39. The paramagnetic properties of O2

40. s*s *p 2p 2p sp p s*s 2s 2s AO of N AO of O ss The MO diagram for NO Energy possible Lewis structures MO of NO

41. benzene, C6H6 10.8 Delocalized Molecular Orbitals • In larger molecules, bonds are sometimes spread over the entire molecule ozone,O3