Created by Adam R. Johnson (adam_johnson@hmc.edu) and posted on VIPEr in February 2011. Copyright Adam
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Describe the bonding in PF5 by deriving an MO diagram.
1. Derive the LGO’s for sigma bonding in PF5. a) draw the Lewis structure and assign a point
group. b) assign symmetry labels to the atomic orbitals on P (3s and 3p only). c) derive the 5
LGO's for -bonding to the F's using the generator orbital technique* (note that you need to use d
orbitals as generator orbitals for a trigonal bipyramidal geometry, but that does not mean that the
phosphorus actually has d orbitals…). d) draw pictures of the LGO’s, including the symmetry
labels.
2a. Use the LGO’s you derived to construct the MO diagram according to the procedure shown
below. You need not draw the molecular orbitals (step 6), just the MO diagram (follow steps 1-5
from the handout).
2b. Your diagram would be different if I allowed you to use the 3d orbitals on phosphorus for
bonding to the fluorines. Which orbital(s) will you use? Redraw the diagram and describe the
most important differences.
Reminder of the technique for constructing LGO’s:
I Draw a Lewis structure and assign VSEPR geometry
II Assign a point group to the molecular geometry
III determine the central atom’s VB hybrid orbitals for the electronic geometry
IV use the VB hybrid orbitals as generator orbitals
V Generate the LGO’s by taking linear combinations of the ligand -orbitals (lobes) to get an
orbital with the same symmetry as the generator orbital
VI Assign proper symmetry labels from the character table
Reminder of the technique for constructing MO diagrams:
I name the MO diagram and its constituents
II place AO's and LGO’s with relative energies on one sides
III place the correct number of electrons on each side
IV form MO's (bonding, antibonding and non-bonding) and give them symmetry labels
V place electrons in the MO's working from the bottom up
VI be able to draw each MO
The generator orbital technique is described on the “Generating LGOs (SALCs)” in-class activity learning object
on VIPEr (https://www.ionicviper.org/class-activity/generating-lgos-salcs)
*