Chapter 10 Chemical Bonding II

1. Chemistry II Chapter 10Chemical Bonding II

2. Chemical Bonding IIMolecular Shapes

3. Chemical Bonding IIVSEPR Theory • e- groups (lone pairs and bonds) are most stable when they are as far apart as possible – v________ s____ e_______ p_____ r_________ theory • Maximum separation • 3-D representation allows us to predict the shapes and bond angles in the molecule

4. Chemical Bonding IIVSEPR Theory e.g. draw the 2 possible Lewis dot structures for NO2- and discuss the behavior of the associated e- groups there are _____ e- groups on N ____ lone pair ____ single bond ____ double bond (counted as 1 group)

5. Chemical Bonding II2 e- Groups: Linear Geometry • 5 basic shapes of molecules: linear, trigonal planar, tetrahedral, trigonal bipyramidal, octahedral

6. Chemical Bonding II2 e- Groups: Linear Geometry • Draw both 2-dimensional and 3-dimensional pictures of the molecules in the following slides

7. Chemical Bonding II2 e- Groups: Linear Geometry • occupy positions opposite, around the central atom linear geometry- bond angle is ________ e.g. CO2

8. Chemical Bonding II3 e- Groups: Trigonal Geometry • occupy triangular positions trigonal planar geometry- bond angle is __________ e.g. BF3

9. Chemical Bonding II3 e- Groups: Trigonal Geometry e.g. Formaldehyde, CH2O 3 e– groups around central atom – why not 120° ?

10. Chemical Bonding II4 e- Groups: Tetrahedral Geometry • occupy tetrahedron positions around the central atom tetrahedral geometry - bond angle is ________ e.g. CH4

11. Chemical Bonding II5 e- Groups: Trigonal Bipyramidal Geometry • occupy positions in the shape of a two tetrahedra that are base-to-base trigonal bipyramidal geometry e.g. PCl5

12. Chemical Bonding II 6 e- Groups: Octahedral Geometry • occupy positions in the shape of two square-base pyramids that are base-to-base octahedral geometry e.g. SF6

13. Chemical Bonding II 3 e- Groups with Lone Pairs: Derivative of Trigonal Geometry • when there are 3 e- groups around central atom, and 1 of them is a lone pairtrigonal planar - bent shape- bond angle < 120° e.g. SO2

14. Chemical Bonding II 4 e- Groups with Lone Pairs : Derivatives of Tetrahedral Geometry • when there are 4 e- groups around the central atom, and 1 is a lone pairtrigonal pyramidal shape –bond angle is 107 ° e.g. NH3

15. Chemical Bonding II 4 e- Groups with Lone Pairs: Derivatives of Tetrahedral Geometry • when there are 4 e- groups around the central atom, and 2 are lone pairstetrahedral-bent shape –bond angle is 104.5 ° e.g. H2O

16. Chemical Bonding II Tetrahedral-Bent Shape

18. Chemical Bonding II 5 e- Groups with Lone Pairs Derivatives of Trigonal Bipyramidal Geometry • when there are 5 e- groups around the central atom, and some are lone pairs, they will occupy the equatorial positions because there is more room • when there are 5 e- groups around the central atom, and 1 is a lone pair, the result is called see-saw shape • aka distorted tetrahedron • when there are 5 e- groups around the central atom, and 2 are lone pairs, the result is called T-shaped • when there are 5 e- groups around the central atom, and 3 are lone pairs, the result is called a linear shape • the bond angles between equatorial positions is < 120° • the bond angles between axial and equatorial positions is < 90° • linear = 180° axial-to-axial

19. Chemical Bonding II Replacing Atoms with Lone Pairsin the Trigonal Bipyramid System

20. Chemical Bonding II See-Saw Shape

21. Chemical Bonding II T-Shape

22. Chemical Bonding II Linear Shape Tro, Chemistry: A Molecular Approach

23. Chemical Bonding II 6 e- Groups with Lone Pairs: Derivatives of Octahedral Geometry • when there are 6 e- groups around the central atom, and 1 is a lone pair, the result is called a square pyramid shape • the bond angles between axial and equatorial positions is < 90°

24. 6 e- Groups with Lone Pairs Derivatives of Octahedral Geometry • when there are 6 e- groups around the central atom, and 2 are lone pairs, the result is called a square planar shape • the bond angles between equatorial positions is 90°

26. Chemical Bonding II Predicting the Shapes Around Central Atoms 1. Draw the Lewis Structure 2. Determine the Number of Electron Groups around the Central Atom 3. Classify Each Electron Group as Bonding or Lone pair, and Count each type remember, multiple bonds count as 1 group 4. Use Table 10.1 to Determine the Shape and Bond Angles

27. Practice – Predict the Molecular Geometry and Bond Angles in ClO2F (Chloryl Fluoride)

28. Practice – Predict the Molecular Geometry and Bond Angles in ClO2F Cl Least Electronegative 4 Electron Groups on Cl Cl Is Central Atom 3 Bonding Groups 1 Lone Pair Cl = 7e─ O2 = 2(6e─) = 12e─ F = 7e─ Total = 26e─ Shape = Trigonal Pyramidal Bond Angles O-Cl-O < 109.5° O-Cl-F < 109.5°

29. Chemical Bonding II Representing 3-Dimensional Shapes on a 2-Dimensional Surface • one of the problems with drawing molecules is trying to show their dimensionality • by convention, the central atom is put in the plane of the paper • put as many other atoms as possible in the same plane and indicate with a straight line • for atoms in front of the plane, use a solid wedge • for atoms behind the plane, use a hashed wedge

31. F F F S F F F SF6

33. Multiple Central Atoms • many molecules have larger structures with many interior atoms • we can think of them as having multiple central atoms • when this occurs, we describe the shape around each central atom in sequencee.g. acetic acid shape around left C is tetrahedral shape around center C is trigonal planar shape around right O is tetrahedral-bent

34. Describing the Geometryof Methanol

35. Describing the Geometryof Glycine

36. Practice – Predict the Molecular Geometries in H3BO3 Tro, Chemistry: A Molecular Approach

37. Practice – Predict the Molecular Geometries in H3BO3 oxyacid, so H attached to O 3 Electron Groups on B 4 Electron Groups on O B Least Electronegative B has 3 Bonding Groups 0 Lone Pairs O has 2 Bonding Groups 2 Lone Pairs B Is Central Atom B = 3e─ O3 = 3(6e─) = 18e─ H3 = 3(1e─) = 3e─ Total = 24e─ Shape on B = Trigonal Planar Shape on O = Bent

38. Practice – Predict the Molecular Geometries in C2H4 Tro, Chemistry: A Molecular Approach

39. Practice – Predict the Molecular Geometries in C2H4 3 Electron Groups on C C = 2(4e─) = 8e ─ H = 4(1e─) = 4e─ Total = 12e─ 0 Lone Pairs Shape on each C = Trigonal Planar

40. Practice – Predict the Molecular Geometries in CH3OCH3

41. Practice – Predict the Molecular Geometries in Dimethyl Ether (CH3OCH3) 4 Electron Groups on C C = 2(4e─) = 8e ─ H = 6(1e─) = 6e─ O = 6(1e─) = 6e─ Total = 20e─ 2 Lone Pairs on O Shape on each C = Tetrahedral Shape on O = Bent

42. Reminder about Eletronegativity! • Electronegativity, is a chemical property that describes the tendency of an atom to e- towards itself

43. Polarity of Molecules • in order for a molecule to be polar it must • have polar bonds • electronegativity difference • dipole moments (charge x distance) • have an unsymmetrical shape • vector addition • polarity affects the intermolecular forces of attraction • therefore boiling points and solubilities • like dissolves like • nonbonding pairs strongly affect molecular polarity

44. Molecule Polarity The H-Cl bond is polar Bonding e- are pulled toward the Cl end of the molecule Net result is a polar molecule.

45. Vector Addition

47. Molecule Polarity The O-C bond is polar The bonding e- are pulled equally toward both O’s Symmetrical molecule Net result is a nonpolar molecule

48. Molecule Polarity The H-O bond is polarBoth sets of bonding e- are pulled toward the O Net result is a polar molecule

49. Molecule Polarity

50. Molecule Polarity The H-N bond is polar All the sets of bonding electrons are pulled toward the N Not symmetrical Net result is a polar molecule