Question 13.14: Structures of Molecules with Multiple Bonds Predict the mole...
Structures of Molecules with Multiple Bonds
Predict the molecular structure of the sulfur dioxide molecule. Is this molecule expected to have a dipole moment?
First, we must determine the Lewis structure for the S O_{2} molecule, which has 18 valence electrons. The expected resonance structures are
To determine the molecular structure, we must count the electron pairs around the sulfur atom. In each resonance structure, the sulfur has one lone pair, one pair in a single bond, and one double bond. Counting the double bond as one pair yields three effective pairs around the sulfur. According to Table 13.8, a trigonal planar arrangement is required, yielding a V-shaped molecule:
Thus the structure of the S O_{2} molecule is expected to be V-shaped with a 120- degree bond angle. The molecule has a dipole moment directed as shown:
Since the molecule is V-shaped, the polar bonds do not cancel.
Table 13.8
Arrangements of Electron Pairs Around an Atom Yielding Minimum Repulsion
|
Number of Electron Pairs |
Arrangement of
Electron Pairs |
Example |
|
|
| 2 | Linear |  |
 |
|
| 3 | Trigonal planar |  |
 |
|
| 4 | Tetrahedral |  |
 |
|
| 5 | Trigonal
bipyramidal |
 |
 |
|
| 6 | Octahedral |  |
 |
