Saturday, March 28, 2009
1.18 - VSPER Theory Shape Rules
1. Draw the Lewis structure for the molecule or ion.
2. Count the total number of regions of high electron density (bonding and unshared electron pairs) around the central atom.
* Double and triple bonds count as ONE REGION OF HIGH ELECTRON DENSITY.
* An unpaired electron counts as ONE REGION OF HIGH ELECTRON DENSITY.
* For molecules or ions that have resonance structures, you may use any one of the resonance structures.
3. Identify the most stable arrangement of the regions of high electron density as ONE of the following:
* linear (2 regions)
* trigonal planar (3 regions)
* tetrahedral (4 regions)
* trigonal bipyramidal (5 regions)
* octahedral (6 regions)