Submitted by John Lee / University of Tennessee Chattanooga on Tue, 06/18/2013 - 09:43
My Notes
Description

All chemistry is learned best by "doing," and I believe this is especially true for determining molecular symmetry.  This activity was designed to end a three-part lecture/activity on symmetry and point groups for my advanced inorganic class.  I call this unit on symmetry a lecture/activity series because it was designed to be student-guided learning and requires the students to teach each other how to determine a molecular point group.  I only gave one formal lecture on symmetry and point groups, which was followed by the symmetry scavenger hunt activity LO.  Finally this assignment was done for a grade to complete the unit.

Here the students are given the assignment one week in advance when starting the unit on symmetry.  They were told what to expect on the due date, which is also in the directions.  The day the assignment was due groups, which were already determined based on lab partners, took turns going to the front of the class to teach us how they determined the point group of the molecule I choose for them at random.  They could use whatever tools needed, which included a large model kit I brought with me, to answer the question. 

Attachment Size
Point group problems.doc 122.5 KB
Learning Goals

A student should be able to apply his/her knowledge of general and inorganic chemistry to:

1.  Draw a correct Lewis structure based on formal charge

2.  Know the different symmetry elements and how to distinguish

3.  How to apply symmetry elements and walk through a flow chart

4.  Be able to determine when it is okay to assume a group (e.g., a methyl, phenyl, NH3) or ligand (e.g, mesitylene, Cp) is rapidly spinning for symmetry equivalence

5.  Determine a likely point group for a molecule

Equipment needs

Large or small molecular model kit

Document camera or computer

 

Implementation Notes

I gave this assignment out the day we started symmetry in lecture along with a due date.  That day I gave a lecture on symmetry elements and how to determine a point group.  The class ended with me working a lot of examples and showing the Otterbein website.  Next class we did the symmetry scavenger hunt and I told the class to begin working on this assignment (if they hadn't already).  In order to give them more time to work on the assigment I moved on to the next topic in class, which put the due date one week from handing out the assignment.  It took all 50 minutes of class for the students to work through their point group assignments.  Since it was a relatively large class, I had them work in pairs and there were 9 groups.  My preference would be to avoid this because one student pretty much took over the discussion.  If it has to be done again due to class size I will be more strict in making them take turns in their discussion.

For those who struggled some I did walk them through by asking leading questions such as rotate the molecule this way or look down this axis, etc...

Another fun implementation I might do next time is to have the problems in a hat and the students choose instead of me. 

Also, I brought in a small molecular model kit and the large kit.  The large model kit worked very well.  Of course some of these problems would take all class to build so the students used the document camera and board to show symmetry elements.

 

 

Time Required
50 minutes

Evaluation

Evaluation Methods

I choose to use this as a completion grade counted as a homework assignment.  However, you could make this more challenging and add a check box for each symmetry element you would like the student to show.

 

 

Evaluation Results

Overall, the students did very well with this assignment.  Many expressed that this was a good follow up to the symmetry scavenger hunt activity.  As expected when I picked the problems, only two structures gave them issues, which are the staggered ferrocene and the [Co(en)3]3+ structures.

Furthermore, only 2 out of 18 students missed the point group questions on the test covering this material, which I believe is related to both this activity and the scavenger hunt.

Creative Commons License
Attribution, Non-Commercial, Share Alike CC BY-NC-SA
Laurel Goj Habgood / Rollins College

I adapted the content of the worksheet by removing the comments specifically related to John's class and used it as a homework assignment.  I was pleasantly surprised how well the class did overall.  I believe it strengthened their ability to determine point groups beyond simple molecules and see the types of complexes they will encounter more frequently as the semester unfolds. 

Mon, 02/16/2015 - 11:53 Permalink