Title: 1
Author: Darren Hage
Last saved by: Jennifer Halverson
Company: MSCTC-FF

Bonding Lab
Lewis Structures and Molecular Shapes

1.	Summarize in your own words the rules for writing Lewis electron-dot structures.  Use and example of a simple molecule (not SO_2, CO_2, or H_2O) to illustrate the application of these rules.  NO3-       . .
                           : O :    Is that only valence electrons are included in the lewis structure.
                       |
                      N
                    //   \
                 :O:   :O:
                          ``
2.	For the molecule you used in example in Question1 above, explain the reasoning in how the VSEPR theory would be used to deduce the geometric shape of this molecule. 

Procedure: 
For each molecule in the table below, list the number of total valence electrons in the molecule, draw the Lewis structure, indicate the molecular geometric shape and the approximate bond angles in the molecule.  Look each shape up on one of the following websites: 
Molecule | Valence Electrons | Lewis Structure | Geometric Shape | Approximate Bond Angles | Sketch

CF_4

4+4(7)=32

..
             : F :
       ..      |      ..
     : F – C --  F :
      ``      |      ``
            : F :
              ``

Tetrahedral

NH_3

5+3(1)=8

..
H – N – H
|
               H

Trigonal Pyramid

SO_4^2-

6+4(6)+2=32

__                     __2-
|              ..           |
|            :O:          |
|      ..      |     ..     |
|    : O – S – O :   |
|      ``     |     ``     |
|            :O:          |
|__         ``        __|

Tetrahedral

NH_4^+

5+4(1)-1=8

_                     _
|                       |  +
|           H         |   
|            |          | 
|    H – N – H   | 
|           |           |  
|          H          |  
|_                  _|

Tetrahedral

H_2S

2(1)+6=8

..
H – S – H
                ``

Linear

PO_4^3- | | | | |
HCl | 1+7=8 | | | |

NF_3

5+3(7)=26

. .
               N
             /  |  \
         :F: :F: :F:
          ``   ``   ``

Tetrahedral
Trigonal pyramid

SiH_4

4+4(1)=8

..
:H:
          ..    |    ..
        :H –Si--H:
         ``    |    ``
              :H:
               ``

Tetrahedral

BF_3

3+3(7)=24

. . 
B
             /  |  \
          :F: :F: :F:
           ``   ``  ``

Tetrahedral

C_2H_6
_see _note

2(4)+6(1)=14

H      H
           |       |
 H --- C ---- C --- H
          |        | 
         H       H

C_2H_4
_see _note

2(4)+4(1)=12

H               H
        \             /
         C====C
        /              \
      H                H

CH_2O | | | | |
Note: molecules C_2H_6 and C_2H_4 have 2 central atoms (carbons are bonded to each other).  Look at the geometric shape on a single carbon.

Questions:
1.	In the last 2 molecules you were asked to examine, there were multiple bonds present.  How does the presence of a multiple bond (double or triple bond) affect your determination of the geometry of the molecule?  Use C_2H_4 or CH_2O to illustrate your discussion. 
2.	Although models cannot show this simply, for molecules like NF_3 (whose structure you drew earlier), the actual bond angles may not exactly equal the angles predicted by VSEPR theory.  For example, the F-N-F bond angles in NF_3 are less than the 109.5° tetrahedral angle.  Why do you think this might be so?