Physical Chemistry: Quantum Mechanics

9 Oct 2019

Fourier Transform IR Spectroscopy of Tetrahedral Borate Ions

Submitted by Zachary Tonzetich, University of Texas at San Antonio
Evaluation Methods: 

The students perpare laboratory reports displaying their data in proper format with each peak labeled. The report must also contain answers to all of the quetions posed in the manual. Student performance and learning is assessed by the qualtity of their written reports and by a separate quiz covering aspects of vibrational spectroscopy. Teaching assistans also ensure that students' data acquisition is performed in a satisfactory manner during the laboratory period.

Evaluation Results: 

Students typically have great difficulty connecting the idea of normal modes, their symmetries, and why we observe IR peaks. They approach IR spectroscopy in much the same way they do NMR spectroscopy (i.e. methane shows four equivalent C-H bonds so I expect one C-H stretching motion) leading to serious misconceptions. This laboratory was designed in part to dispell these misconceptions. Question 1 addresses this issue most directly and many of the class answer incorrectly.

The questions in the laboratory involving harmonic oscialltor analysis are generally more straightforward for students as they just need to use the correct equations. Most of the class answers these correctly.

Likewise, students generally understand that vibrational frequencies are inversely proportional to the mass of the atoms involved in the vibration and are there able to make connections between the observed spectra of BH4-, BD4- and BF4-.

Aspects of functional group analysis are more familiar to students and they generally have little trouble assigning the spectrum of tetraphenylborate.

Description: 

This experiment was developed for an upper division Instrumental Analysis course to give students additional experience with infrared (IR) spectroscopy beyond the routine functional group identification encountered in undergraduate Organic Chemistry courses. It shares some aspects with the analysis of gas phase rovibrational spectra typically performed in Physical Chemistry courses, but places a greater emphasis on more practical considerations including data acquisition (using ATR) and interpretation. The molecular ions used in the experiment also demonstrate tetrahedral symmmetry which allows for topics in Group Theory to be exploited.

The experiment has students record the spectra of several tetrahedral borate ions including the isotopomers NaBH4 and NaBD4. The students then analyze their data in the context of the symmetry of normal modes, the harmonic osciallator model, comparisons with Raman spectra, and functional group composition. Post lab questions guide students through each of the topics and ask them to make quantative and qualitative predictions based on their data and theoretical models of molecular vibration.

Course Level: 
Learning Goals: 

-Students should be able to understand the relationship between molecular structure, normal modes, and peaks in the IR spectrum. This is a major misconception with students as they tend to believe that the presence of four B-H bonds in the borohydride ion will neccessary mean that four peaks (or one since they are equivalent) will be observed by IR. Unlike NMR spectroscopy, there is no 1:1 correspondence between the number of equivalent bonds and the number of peaks observed in the spectrum.

-Students should also be able to apply their knowledge of theoretical models (quantum harmonic oscillator) to quantitaively intrepret IR spectra and predict the energy of transitions that cannot be observed due to instrumental limitations.

-Students should be able to understand at a qualitative level how the masses of atoms affect the energy of molecular vibrations.

Equipment needs: 

The only required piece of equipment beyond the chemicals is an infrared spectrophotometer. At our institution we use an ATR element to acquire the data, but KBr pellets or nujol mulls should work equally well. All chemicals were purchased from Sigma-Aldrich and are of reasonable price.

Implementation Notes: 

See attached file with more details. The data acquisition is very straightforward if ATR sampling is employed. Students need only use the instrument for about 15 - 20 minutes to record all four samples.

Time Required: 
30 minutes to 2 hr depending upon the number of students.
8 Jun 2019

VIPEr Fellows 2019 Workshop Favorites

Submitted by Barbara Reisner, James Madison University

During our first fellows workshop, the first cohort of VIPEr fellows pulled together learning objects that they've used and liked or want to try the next time they teach their inorganic courses.

6 Jun 2019
Evaluation Methods: 

The guided reading questions may be graded using the answer key. 

Evaluation Results: 

These questions have not yet been assigned to students.

Description: 

Guided reading and in-class discussion questions for "High-Spin Square-Planar Co(II) and Fe(II) Complexes and Reasons for Their Electronic Structure."

Course Level: 
Learning Goals: 

1.  Bring together ligand field theory and symmetry.

  1. Students should be able to identify symmetry of novel molecules in the literature.

  2. Students should be able to explain d-orbital ordering in a coordination complex using ligand field theory.

  3. Students should be able to identify donor/acceptor properties of previously unseen ligands.

  4. Students should be able to apply your knowledge of electronic transitions to the primary literature.

  5. Students should be able to become more familiar with 4-coordinate geometries.

  6. Students should be able to predict magnetic moments of high-spin and low-spin square-planar complexes.

  7. Students should be able to identify properties of ligands that favor formation of the highly unusual high-spin square planar complexes.

2.  Students should comfortable with reading and understanding primary literature.


 

Related activities: 
Implementation Notes: 

You do not have to assign all of the guided reading questions at once.  You may consider assigning questions as they pertain to where you are in your inorganic chemistry class.

Time Required: 
this has not been used yet for in-class discussion.
30 Jun 2016

Basics of Lanthanide-Based Photophysics

Submitted by Jacob Charles Lutter, University of Michigan
Description: 

This 5 slides about outlines the basics of lanthanide photophysics as a primer for those new to the topic.  These properties are very unique and actually very useful, which is a topic for another time.  The intricacies of what causes the Ln luminescence, its strengths and drawbacks are discussed along with how these drawbacks are addressed in molecular complexes.  Notes for the instructor are included that explain each slide.

Prerequisites: 
Course Level: 
Learning Goals: 

Students should be able to explain the Laporte selection rule, and why it is so important to the Ln photophysical properties of absorption/excitation and lifetimes.

Students should be able to explain how the intrinsic nature of the 4f orbitals creates advantages and disadvantages for luminesecence.

Students should be able to design possible antenna ligands based on desired characteristics.

Subdiscipline: 
Implementation Notes: 

Feel free to use all or part of this presentation as you see fit. 

27 Jun 2016

Student Oral Presentations of a Communication from the Primary Literature

Submitted by Carmen Works, Sonoma State University
Evaluation Methods: 

see rubric that is attached 

Description: 

In the humanities it is common practice to read a piece of literature and discuss it.  This is also practiced in science and is the purpose of this exercise.  Each student is assigned a communication from the current  literature (inorganic, JACS, organometallics, J. Phys. Chem) and the student presents this paper to the class.  The class will also have the opportunity to read the article prior to the presentation, and I post each paper on my LMS page.  The presenter will be responsible for explaining the paper, and leading a critical discussion.  This is not an easy assignment since these papers are filled with chemical jargon, but an important part of their chemical education is to be able to tackle the literature.  In addition a lot of this jargon is covered during the semester.

  

 

Course Level: 
Learning Goals: 

·      Students will learn to read a paper from the primary literature

·      Students will learn to present the a paper from the primary literature

·      Students will learn to create a group discussion

·      Students will learn how to relate chemical jargon learned throughout the four years of chemistry to the literature

·      Students will learn how to answer exam questions from the primary literature

 

Implementation Notes: 

I hand out selected communications during the second week of class.  Students are allowed to swap papers. They have the entire semester to read the paper and prepare a talk but the talks are during the last 3 weeks of class.  Each student is give 25 min to present their paper to the class.  The assignment is graded using the attached rubric and is worth 15% of their final grade.  I selected about 7 exam questions for the final exam and ask students to answer 5 of these questions.  I try to structure the questions so that they don't have to "know" every paper.  I have attached an example of such a question.  

27 Mar 2016

Isotopic labeling and reduced mass calculations for IR spectroscopy

Submitted by Adam R. Johnson, Harvey Mudd College
Evaluation Methods: 

as this was done in class, I evaluated each group's presentation in real time as they presented it to the class. I used 2a and 3 in my class this year, and will likely use the others on an exam.

Evaluation Results: 

for 2a, the students did not have much trouble determining the fact that the 18O peaks were shifted by the correct amount, thus verifying the assignment. They, by inspection, were able to determine that the two peaks were in-phase and out-of-phase stretches (symmetric and antisymmetric).

for 3, at first the students struggled with what the problem was asking. Some of them wanted to calculate the force constants. I didn't followup to see if that made sense but it seems likely that the force constants would indicate stronger bond to the O than the S or Se. Of course, that would be true given the relative magnitudes of the stretches, and evaluating whether or not the Mo=O linkage is "stronger than expected" is not something that I would be able to predict. However, once I got them on track of predicting the Mo=S and Mo=Se stretches from the Mo=O (and the other combinations), they agreed it made sense. They weren't sure whether 10% agreement was "close" or not, which is fair. But certainly the oxo does a worse job predicting the others.

Description: 

I used this as an in class activity but it may work better as a problem set for your class. I had the students read the pertinent chapters of the textbook which go through symmetry and molecular vibrations, including using both stretches and cartesian axes as bases. In class, I divided the students up into four groups. Each group did one of the problems for 30 minutes and during the last 20 minutes of class, they reported out their solution. The students had not seen the Hooke’s law in the textbook so I included it as part of the activity. I also included a handout on applying the group theory to molecular motions.

Learning Goals: 

A student should be able to use the Cartesian axes as a basis for molecular motion

A student should be able to use a bond vector as a basis for a molecular vibration

A student should be able to, given an IR stretch, predict a stretch after an isotopic substitution

Equipment needs: 

a set of character tables (C2v, C3v and C4v at a minimum) is needed for some of the groups

Prerequisites: 
Course Level: 
Implementation Notes: 

I did this as an in-class activity on 3/28/2016. I had 15 students, so groups of 3-4 on each of 4 problems. I used problem 2a, 3, and the two related LOs in class.

Time Required: 
1 50 minute class period
2 Jul 2015
Evaluation Methods: 

Students can hand in tthe first set of questions as homework which may be evaluated.  Class participation and group work may also be graded appropriately.

Evaluation Results: 

This is an untested LO.

Description: 

This learning object is based on discussion of the literature, but it follows a paper through the peer review process.  Students first read the original submitted draft of a paper to ChemComm that looks at photochemical reduction of methyl viologen using CdSe quantum dots.  There are several important themes relating to solar energy storage and the techniques discussed, UV/vis, SEM, TEM, electrochemistry, and catalysis, can be used for students in inorganic chemistry.

Unlike a typical literature LO where students discuss only the current science, this LO contains the actual reviewer comments to the original submitted manuscript as well as a link to the final version that was published in Journal of Materials Chemistry A.

DOI: 10.1039/C5TA03910J

Prerequisites: 
Learning Goals: 

Students will be able to...

·  Communicate the main ideas of a scientific research paper to classmates.

·  Identify the research area, importance of the research, and background information provided in a scientific paper.

·  Discuss areas of a paper that may be improved through revision.

·  Compare their views of necessary revisions with actual anonymous reviewers on a scientific paper and the eventual publication.

·  Understand the importance and shortcomings of the peer review process using an actual publication from the literature.

Implementation Notes: 

The LO has multiple sections which may be discarded or edited depending on the particular learning goals desired.  While the chemistry may be difficult for lower level students, the discussion of the peer review process may be valuable to students across multiple levels and even in writing courses.  Also provided are the authors' actual responses to the reviewers comments.  It should also be noted that the original article was submitted to ChemComm, but the subsequent revised article was submitted and accepted to Journal of Materials Chemistry A.

Time Required: 
Homework Assignment + 1 h in class

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