Part A: There is a table attached to the end of this document. For each molecule or ion in the table, provide entries for columns I through IX.

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1 Chemistry 400 Discussion: VSEPR Theory and Molecular Shapes Instructions: Work through the exercises below. If you have access to molecular model kits, use them to build three dimensional models of the molecules (or polyatomic ions) in the exercises and to help you answer the questions. Part A: There is a table attached to the end of this document. For each molecule or ion in the table, provide entries for columns I through IX. Column I: Draw the best Lewis structure. Label any atoms with nonzero formal charge. Column II: List the total number of resonance structures and draw at least one resonance structure. Column III: ow many electron groups are around the central atom? Column IV: What is the electron geometry? Column V: What is the molecular geometry? Possible answers: linear, trigonal planar, tetrahedral, trigonal bipyramidal, octahedral, bent, trigonal pyramidal, see-saw, T-shaped, square pyramidal, square planar). Column VI: Give values of the bond angles around the central atom. (for example, 109.5, less than 109.5, 120, less than 120, etc.). Column VII: Give the hybridization of the central atom. Column VIII: State how many sigma bonds and pi bonds are present in the molecule or ion. Part B: More Complex Molecules: The questions below make use of more interesting, and more complex, molecules. Many of these examples have more than one central atom. If you have access to molecular models, build 3-D models of the molecules to help you answer the questions. 1. The figure below shows how the atoms in the nerve agent Tabun are connected to each other. Draw the complete Lewis dot structure shown (include any multiple bonds or lone pairs). Assign the hybridization to each atom (except hydrogens). Give an estimate of the P-C-N angle. O C C O P C N N C C 1

2 2. The molecular formula for ethanol is C 3 C 2 O. Draw its Lewis structure. What is the C-O- angle? What is the hybridization of the oxygen atom? 3. The molecular formula for n-octane is C 8 18 with all of the carbons attached in a row. Draw the skeletal structure and answer the questions below. a. What is its hybridization of every carbon? What is the bond angle about every carbon? b. Do single bonds rotate? If so, redraw n-octane above as small as possible while still keeping the bond angle approximately correct. 4. The molecular formula for ozone is O 3. Draw the best Lewis structure and any resonance structures. Label any atoms with nonzero formal charges and answer the questions below. a. What is the O-O-O bond angle? b. What is the hybridization of the central oxygen atom? 2

3 5. The molecular formula for acetic acid is C 3 COO. a. Draw the best Lewis structure. b. What is the hybridization of each of the carbon atoms and the oxygen atom bonded to the hydrogen? 6. The molecular formula for the acetate ion is C 3 COO. Draw all possible valid resonance structures. Label all nonzero formal charges. Label all of the bonds, including bonds that contain partial - character that arise from resonance. Describe the true nature of the carbon oxygen bond in acetate. 7. The structure below is the molecule adrenaline (also called epinephrine). Draw the complete Lewis structure of adrenaline showing all of the atoms (including hydrogens) and lone pairs. Give an estimate of the bond angles involving the carbon atoms in the ring. O O O N C 3 3

4 8. Kevlar is a very strong material that is used in bullet-proof vests and many other applications. It is an example of a class of compounds called polymers which are large molecules made up of small units (monomers) linked together to make a huge chain. The structural formula for the repeat unit of Kevlar is shown below. The brackets indicate that the structure shown below is repeated over and over again. O O N N C C n a. Complete the Lewis structure (i.e., add in the lone pairs). b. Using skeletal structures, draw 4 repeat units of Kevlar 9. Methyl ethyl ketone (MEK) is a solvent that is sometimes used in the Navy for cleaning and degreasing ships. The molecular formula is C 3 C(O)C 2 C 3. The O atom is in parentheses to indicate that it is branched off of the second carbon atom. a. Draw the best Lewis structure. b. Give an estimate of the C-C-O bond angles. c. ow many bonds are there? 4

5 Formula I: Best LS w/ nonzero FC shown II: Total # resonance structures, draw 1 III: e- groups CN Don t answer IV: e- geom. V: Molec. geom. VI: bond angles VII: hybridzation VIII: #, # CO2 NO3 SO2 CO3 2 BCl3

6 Formula SO4 2 I: Best LS w/ nonzero FC II: Total #RS, draw 2 III: e- groups IV: e- geom. V: Molec. geom. VI: bond angles VII: hybridzation VIII: #, # C3Cl N3 PCl5 SF6