- Draw the Lewis structure for the molecule or ion.
- 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
Test My Knowledge
- Identify the most stable arrangement of the regions of high electron density as ONE of the following:
- trigonal planar
- trigonal bipyramidal
- Determine the positions of the atoms based on the types of electron pairs present (i.e., bonding pairs vs. unshared pairs). For trigonal bipyramidal and octahedral arrangements, there can sometimes be more than one possible arrangement of the bonding and unshared pairs:
- Trigonal bipyramidal - place any unshared pairs in the plane of the triangle.
- Octahedral - if you have two unshared pairs, place them on opposite sides of the central atom.
- Identify the molecular structure based on the positions of the ATOMS (NOT on the regions of high electron density).