Chemical Bonding II: Molecular Geometry and Hybridization of Atomic Orbitals

1. Chemical Bonding II:Molecular Geometry and Hybridization of Atomic Orbitals Chapter 10

2. 10.1

3. Molecular Shapes Valence Shell Electron-Pair Repulsion (VSEPR) Theory Each group of valence electrons around a central atom is located as far away from the others as possible in order to minimize repulsion. An electron group may be a single, double, or triple bond or a lone pair.

4. Balloon Analogy for the MutualRepulsion of Electron Groups Two Three Four Five Six Number of Electron Groups

6. First we will look at examples where there are no lone pairs of electrons on the central atom. In this case the molecular geometry is the same as the electron geometry.

7. # 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 10.1

8. 0 lone pairs on central atom Cl Be Cl 2 atoms bonded to central atom 10.1

9. # 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 10.1

10. 10.1

11. # 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 10.1

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13. # 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 10.1

14. 10.1

15. # 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 10.1

16. 10.1

17. Chapter 10 Homework 1-5, 7, 8, 10-14, 16-24, 26, 28, 29, 32, 34-36, 41, 42

19. Molecular Shapes You must distinguish between the electron-group arrangement and the molecular shape. The molecular shape is defined by the relative positions of the atomic nuclei. If there are no lone pairs of electrons the molecular shape is the same as the electron-group arrangement. If there are lone pairs the molecular shape is only part of the electron arrangement. The ideal bond angles are determined by the electron-group angles.

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

21. # 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 SO2 10.1

22. # 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 10.1

23. # 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 10.1

24. # of atoms bonded tocentral atom # lone pairs on central atom trigonal bipyramidal seesaw Arrangement ofelectron pairs Molecular Geometry Class VSEPR trigonal bipyramidal trigonal bipyramidal AB5 5 0 AB4E 4 1 SF4 10.1

25. # 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 10.1

26. # 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 10.1

27. 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 10.1

28. 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 10.1

29. What are the molecular geometries of AsH3, OF2, AlCl4-, H3O+, C2H4, SnCl5-, and C2H2? 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. 10.1

30. Molecular Shapes with More Than One Central Atom For more complicated molecules you must give the shape and bond angles around each central atom. Examples: ethanol

31. The Tetrahedral Centers of Ethaneand of Ethanol Ethane Ethanol

32. Polar Molecules - Dipole moments In chapter 9 you learned about covalent bonds that are polar. A polar molecule is one the has a positive end and a negative end. (The center of positive charge and the center of negative charge do not coincide.) A polar molecule is said to have a dipole moment. A molecule with two or more polar bonds can be nonpolar if it is symmetric. Dipole moment = charge x distance

33. 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 10.2

34. 10.2

35. Polarity of CO2 and H2O Water - H2O Carbon Dioxide - CO2 - - - - + .. .. .. .. O O C O .. .. H H A non- polar molecule + + A Polar molecule The bonds are polar, but the molecule is symmetrical, so that the molecule overall is non-polar. The bonds are polar, and the molecule is non-symmetrical.

36. Predicting The Polarity of Molecules Problem: From electronegativity, and their periodic trends, predict whether each of the following molecules is polar and show the direction of bond dipoles and the overall molecular dipole. (a)Phosphine, PH3 (b) Carbon disulfide, CS2 (also OCS) (c) Aluminum chloride, AlCl3 .. .. .. (a) P P P H H H H H H H H H Molecular Dipole Bond dipoles Molecular shape

37. 10.2

38. 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 10.2

39. Which of these are polar? CH4, CCl4, CHCl3,, CH2Cl2, CH3Cl. 10.2

40. Valence Bond Theory Basic Principle of Valence Bond Theory: a covalent bond forms when the orbitals from two atoms overlap and a pair of electrons occupies the region between the nuclei. Usually this means that each bonding orbital should contain one electron. The electrons must have opposite spins. The bond strength depends on the attraction of nuclei for the shared electrons, so the greater the orbital overlap, the stronger the bond.

42. 10.4

43. Change in electron density as two hydrogen atoms approach each other. 10.3

44. The sp Hybrid Orbitals in Gaseous BeCl2

46. Hybridization is the mixing of atomic orbitals in an atom to generate a set of new orbitals called hybrid orbitals. • The total number of orbitals doesn’t change. • Covalent bonds are formed by: • Overlap of hybrid orbitals with atomic orbitals • Overlap of hybrid orbitals with other hybrid orbitals

49. 10.4

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