Chemical Bonding II: Molecular Geometry and Hybridization of Atomic Orbitals

1. Chemical Bonding II:Molecular Geometry and Hybridization of Atomic Orbitals Chapter 9 February 28th, 2005

3. # of atoms bonded tocentral atom # lone pairs on central atom Arrangement ofelectron pairs Molecular Geometry Class linear linear B B Valence shell electron pair repulsion (VSEPR) model: Predict the geometry of the molecule from the electrostatic repulsions between the electron (bonding and nonbonding) pairs. AB2 2 0

4. 0 lone pairs on central atom Cl Be Cl 2 atoms bonded to central atom

5. # of atoms bonded tocentral atom # lone pairs on central atom trigonal planar trigonal planar Arrangement ofelectron pairs Molecular Geometry Class VSEPR AB2 2 0 linear linear AB3 3 0

7. # of atoms bonded tocentral atom # lone pairs on central atom trigonal planar trigonal planar AB3 3 0 Arrangement ofelectron pairs Molecular Geometry Class tetrahedral tetrahedral VSEPR AB2 2 0 linear linear AB4 4 0

9. # of atoms bonded tocentral atom # lone pairs on central atom trigonal planar trigonal planar AB3 3 0 Arrangement ofelectron pairs Molecular Geometry Class trigonal bipyramidal trigonal bipyramidal VSEPR AB2 2 0 linear linear tetrahedral tetrahedral AB4 4 0 AB5 5 0

11. # of atoms bonded tocentral atom # lone pairs on central atom trigonal planar trigonal planar AB3 3 0 Arrangement ofelectron pairs Molecular Geometry Class trigonal bipyramidal trigonal bipyramidal AB5 5 0 octahedral octahedral VSEPR AB2 2 0 linear linear tetrahedral tetrahedral AB4 4 0 AB6 6 0

13. lone-pair vs. lone pair repulsion lone-pair vs. bonding pair repulsion bonding-pair vs. bonding pair repulsion > >

14. # of atoms bonded tocentral atom # lone pairs on central atom Arrangement ofelectron pairs Molecular Geometry Class trigonal planar bent VSEPR trigonal planar trigonal planar AB3 3 0 AB2E 2 1

15. # of atoms bonded tocentral atom # lone pairs on central atom Arrangement ofelectron pairs Molecular Geometry Class trigonal pyramidal tetrahedral VSEPR tetrahedral tetrahedral AB4 4 0 AB3E 3 1

16. # of atoms bonded tocentral atom # lone pairs on central atom trigonal pyramidal Arrangement ofelectron pairs Molecular Geometry AB3E 3 1 tetrahedral Class bent tetrahedral O H H VSEPR tetrahedral tetrahedral AB4 4 0 AB2E2 2 2

17. # of atoms bonded tocentral atom # lone pairs on central atom trigonal bipyramidal distorted tetrahedron Arrangement ofelectron pairs Molecular Geometry Class VSEPR trigonal bipyramidal trigonal bipyramidal AB5 5 0 AB4E 4 1

18. # of atoms bonded tocentral atom # lone pairs on central atom trigonal bipyramidal distorted tetrahedron Arrangement ofelectron pairs Molecular Geometry AB4E 4 1 Class trigonal bipyramidal T-shaped F F Cl F VSEPR trigonal bipyramidal trigonal bipyramidal AB5 5 0 AB3E2 3 2

19. # of atoms bonded tocentral atom # lone pairs on central atom trigonal bipyramidal distorted tetrahedron Arrangement ofelectron pairs Molecular Geometry AB4E 4 1 Class trigonal bipyramidal T-shaped AB3E2 3 2 trigonal bipyramidal linear I I I VSEPR trigonal bipyramidal trigonal bipyramidal AB5 5 0 AB2E3 2 3

20. octahedral octahedral AB6 6 0 # of atoms bonded tocentral atom # lone pairs on central atom square pyramidal octahedral Arrangement ofelectron pairs Molecular Geometry Class F F F Br F F VSEPR AB5E 5 1

21. octahedral octahedral AB6 6 0 # of atoms bonded tocentral atom # lone pairs on central atom square pyramidal octahedral AB5E 5 1 Arrangement ofelectron pairs Molecular Geometry Class square planar octahedral F F Xe F F VSEPR AB4E2 4 2

22. What are the molecular geometries of SO2 and SF4? F S F F O O S F Predicting Molecular Geometry • Draw Lewis structure for molecule. • Count number of lone pairs on the central atom and number of atoms bonded to the central atom. • Use VSEPR to predict the geometry of the molecule. AB4E AB2E distorted tetrahedron bent

23. F H d- d+ Dipole Moments and Polar Molecules electron rich region electron poor region m = Q x r Q is the charge r is the distance between charges 1 D = 3.36 x 10-30 C m

26. Which of the following molecules have a dipole moment? H2O, CO2, SO2, and CH4 O O S H H H O O O C H H C H dipole moment polar molecule dipole moment polar molecule no dipole moment nonpolar molecule no dipole moment nonpolar molecule

28. Dipoles (polar molecules) and Microwaves

29. How does Lewis theory explain the bonds in H2 and F2? Overlap Of 2 1s Bond Dissociation Energy Bond Length 2 2p H2 436.4 kJ/mole 74 pm F2 150.6 kJ/mole 142 pm Sharing of two electrons between the two atoms. Valence bond theory – bonds are formed by sharing of e- from overlapping atomic orbitals.

31. Change in electron density as two hydrogen atoms approach each other.

32. If the bonds form from overlap of 3 2p orbitals on nitrogen with the 1s orbital on each hydrogen atom, what would the molecular geometry of NH3 be? Valence Bond Theory and NH3 N – 1s22s22p3 3 H – 1s1 If use the 3 2p orbitals predict 900 Actual H-N-H bond angle is 107.30

33. Hybridization – mixing of two or more atomic orbitals to form a new set of hybrid orbitals. • Mix at least 2 nonequivalent atomic orbitals (e.g. s and p). Hybrid orbitals have very different shape from original atomic orbitals. • Number of hybrid orbitals is equal to number of pure atomic orbitals used in the hybridization process. • Covalent bonds are formed by: • Overlap of hybrid orbitals with atomic orbitals • Overlap of hybrid orbitals with other hybrid orbitals

36. Predict correct bond angle

37. Formation of sp Hybrid Orbitals

38. Formation of sp2 Hybrid Orbitals

39. How do I predict the hybridization of the central atom? Count the number of lone pairs AND the number of atoms bonded to the central atom # of Lone Pairs + # of Bonded Atoms Hybridization Examples 2 sp BeCl2 3 sp2 BF3 4 sp3 CH4, NH3, H2O 5 sp3d PCl5 6 sp3d2 SF6

42. Pi bond (p) – electron density above and below plane of nuclei of the bonding atoms Sigma bond (s) – electron density between the 2 atoms

46. How many s and p bonds are in the acetic acid (vinegar) molecule CH3COOH? H H C H C O O H Sigma (s) and Pi Bonds (p) 1 sigma bond Single bond 1 sigma bond and 1 pi bond Double bond Triple bond 1 sigma bond and 2 pi bonds s bonds = 6 + 1 = 7 p bonds = 1

47. Experiments show O2 is paramagnetic O O No unpaired e- Should be diamagnetic Molecular orbital theory – bonds are formed from interaction of atomic orbitals to form molecular orbitals.

48. Energy levels of bonding and antibonding molecular orbitals in hydrogen (H2). A bonding molecular orbital has lower energy and greater stability than the atomic orbitals from which it was formed. An antibonding molecular orbital has higher energy and lower stability than the atomic orbitals from which it was formed.