Submitted by Adam Johnson / Harvey Mudd College on Wed, 06/15/2011 - 14:11
My Notes

I use this in-class exercise after I have taught the students how to construct LGOs using the generator orbital technique.  The previous week, they do an in-class exercise on that topic, and this week, they use the LGOs from the previous week to construct MO diagrams.

Attachment Size
polyatomicMO_0.docx 31.25 KB
Learning Goals

Given a centrosymmetric molecule, a student should be able to construct its simplified, σ-only MO diagram.

Related activities
Implementation Notes

The students work in groups of 2 to 3.  Sometimes I match up "weak" and "strong" students and sometimes I let them pick.  I haven't really noticed much difference.  I circulate and give the students hints, and each group puts its MO diagram up at the chalkboard.  If there is time, I have each group go through the construction of the MO diagram, but often I just hit the highlights.

Time Required
one 50 minute class period


Evaluation Methods

I have homework assignments on this exact topic the week after they do this exercise.  I also make sure they know that this WILL be on the midterm and final exam, and I don't disappoint.

Evaluation Results

All students have a complete (and correct) qualitative σ-only MO diagram for their group's molecule by the end of the class period.  I collect each group's MO diagrams and post either the student-generated answer key or my answer key (linked to this LO) after class. 

Some students do really well with this technique, and by the end of my course, I would say that almost all students are able to construct an MO diagram, especially if they are given central atom AOs with symmetry labels, and similarly labeled LGOs.

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