17 Nov 2007

The N5+ Cation: Explosive Chemistry and Raman Analysis

Literature Discussion

Submitted by Maggie Geselbracht, Reed College
Categories
Description: 

­This paper discusses the synthesis and characterization of a novel compound of nitrogen.  The pre-discussion assignment asks students draw a Lewis structure for the N5+ cation, and using the tools of group theory, conduct a normal mode vibrational analysis, comparing the results to the experimental Raman spectral data.­­

AttachmentSize
Microsoft Office document icon N5+ Raman Discussion Questions27.5 KB
Implementation Notes: 

I have used this paper and accompanying discussion assignment as the basis of an in-class literature discussion after we cover the group theory tools for predicting the number of allowed Raman and IR normal modes of vibration for small molecules.  Surprisingly, some students had difficulties drawing valid Lewis structures for this cation, typically starting with an incorrect skeletal structure.  We talk through the answers to the group theory questions, and this is a good way to expose questions and misunderstandings on how to apply these tools before students work additional problems in a problem set.  I also discuss the synthesis briefly with an emphasis on the novelty of this chemistry and challenges in characterizing highly explosive compounds!

Time Required: 
45 minutes of class discussion
Evaluation
Evaluation Methods: 

Students are assigned a series of questions to allow them to practice using group theory to understand the vibrational spectrum of a molecule and thus guide their reading of the paper prior to class discussion.

Evaluation Results: 

The key to success is drawing the correct Lewis structure to predict the correct shape of the molecule.

Creative Commons License: 
Creative Commons Licence

Comments

I've used this literature discussion at the end of my symmetry unit just before going on to MO theory. It is usually the first literature discussion that my students see in inorganic. It's great for that spot in the class because students don't need to know about bonding or transition metals to see why symmetry is cool and useful.Most of my students have had quantum chemistry, so they know about Raman spectroscopy. I absolutely agree that students need to be able to draw a good Lewis structure in order to predict the right point group! It's a good reminder about Lewis structures and VSEPR. Otherwise, students find this paper very accessible. They also like the connection to explosives!

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