Chapter 10 Bonding Theory and Molecular Structure

1. Chapter 10 Bonding Theory and Molecular Structure

2. Molecular Shapes • The VSEPR model • electron-pair geometries • molecular geometries • Molecular polarity • Valence Bond Theory • Covalent bonding and orbital overlap • Hybrid orbitals • sp hybrid orbitals • sp2 hybrid orbitals • sp3 hybrid orbitals • hybridization involving d orbitals • Multiple bonds • double bonds • triple bonds • Molecular Orbital Theory • First-row diatomics • Second-row diatomics • Benzene and Aromatic Compounds

3. Molecular Shapes • The VSEPR model • electron-pair geometries Valence Shell Electron Pair Repulsion Theory: regions of electron density (single, double, or triple bonds or lone pairs) arrange themselves around an atom to be as far apart as possible (electron pair repulsion). Electron pair geometries:

5. Molecular Shapes • The VSEPR model • molecular geometries

6. Molecular Shapes • The VSEPR model • molecular geometries Electron pair geometry: tetrahedral Molecular geometry: tetrahedral trigonal pyramidal bent

11. Molecular Shapes • The VSEPR model • molecular geometries NI3 SO2 PCl4– NO3– OF2 SO32– BrCl3 PO43–

12. Molecular Shapes • Molecular polarity Molecular polarity  physical and chemical properties d+d– bonds: if DX > 0  polar bond A—B molecules and ions: if dipoles do not exactly cancel, molecule will be polar BeCl2 BF3 CH2O CCl4 CHCl3 NH3 dipole

13. Molecular Shapes • Molecular polarity PCl3F2 CO32– CHO2–

14. Valence Bond Theory • Covalent bonding and orbital overlap Bonds are formed using valence electrons and orbitals: overlap atomic orbitals molecular orbitals (covalent bonds) e.g.,

15. Valence Bond Theory • Covalent bonding and orbital overlap But what about CH4? Tetrahedral, all bonds equivalent. How do we get this from s and p a.o.s?

16. Valence Bond Theory • Hybrid orbitals • sp hybrid orbitals BeH2 facts: 2 equivalent bonds

17. Valence Bond Theory • Hybrid orbitals • sp2 hybrid orbitals BH3 facts: trigonal planar, 3 equivalent bonds

18. Valence Bond Theory • Hybrid orbitals • sp3 hybrid orbitals tetrahedral, 4 equivalent bonds CH4 facts:

19. Valence Bond Theory • Hybrid orbitals • sp3 hybrid orbitals

20. Valence Bond Theory • Hybrid orbitals • hybridization involving d orbitals

21. Valence Bond Theory • Hybrid orbitals Summary: e– pair geometry hybridization linear sp trigonal planar sp2 tetrahedral sp3 trigonal bipyramidal sp3d octahedral sp3d2

22. Valence Bond Theory • Hybrid orbitals What is the hybridization of the central atom in each of the following? CCl4 BrCl3 BF3 SF6 NH3 BeCl2 PCl4– XeF4

23. Valence Bond Theory • Multiple bonds • double bonds trigonal planar = sp2 all six atoms lie in same plane C2H4 facts:

24. Valence Bond Theory • Multiple bonds • triple bonds C2H2 facts: linear = sp

25. Valence Bond Theory What is the hybridization of each indicated atom in the following molecule? How many sigma and pi bonds are in the molecule?

26. Molecular Orbital Theory Fact: O2 is paramagnetic! Lewis structure VSEPR Valence bond theory • sp2 hybridized • lone pairs in sp2 hybrid orbitals • bonding pairs in s and p bonds All show all electrons paired.

27. Molecular Orbital Theory Overlap of wave functions: constructive overlap destructive overlap

28. Molecular Orbital Theory • First-row diatomics Overlap of 1s orbitals: s*1s antibonding m.o. (higher energy than separate atoms) s1s bonding m.o. (lower energy than separate atoms)

29. Molecular Orbital Theory • First-row diatomics (no. of e– in bonding m.o.s) - (no. of e– in antibonding m.o.s) 2 bond order = H2 b.o. = 1 (i.e., lower energy than separate atoms)

30. Molecular Orbital Theory • First-row diatomics He2 He2+ b.o. = 0 b.o. = 0.5

31. z z x x y y • Molecular Orbital Theory • Second-row diatomics Overlap of 2s and 2p orbitals 2s s2s and s*2s (same as 1s), then 2p orbitals give: (i.e., 8 a.o.s  8 m.o.s)

32. Molecular Orbital Theory • Second-row diatomics E

33. Molecular Orbital Theory • Second-row diatomics

34. Molecular Orbital Theory • Second-row diatomics

35. benzene C6H6 6 e– in a cyclic, planar p system  aromatic stabilization all sp2 120º • Benzene and Aromatic Compounds planar hexagon

36. naphthalene benzo[a]pyrene (carcinogen) p-dichlorobenzene • Benzene and Aromatic Compounds methylbenzene toluene 1,2-dimethylbenzene ortho-dimethylbenzene (o-xylene) (meta-xylene) (para-xylene)