Molecular Structure and Bonding

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.
29 Jul 2019

Introduction to Drago's ECW Acid-Base Model

Submitted by Colleen Partigianoni, Ferris State University
Description: 

This LO was created to introduce Drago’s ECW model, which is an important contribution to the discussion of Lewis acid-base interactions. Unlike the qualitative Pearson’s HSAB model (Hard Soft Acid-Base model,) the quantitative ECW model can be used to correlate and predict the enthalpies of adduct formation and to obtain enthalpy changes for displacement or exchange reactions involving many Lewis acids and bases.  Unlike all other acid-base models, graphical displays of the ECW model clearly show that there is no one order of acid or base strengths, and illustrate that two parameters are needed for each acid and base to provide an order of acid or base strength.  The ECW model can also provide a measure of steric strain energy or pi bonding stabilization energy accompanying adduct formation, which is not possible with any other acid-base model. 

This set of slides is intended to provide a basic introduction to the model and several examples of predicting energy changes using the model. It also illustrates how to construct and interpret a graphical display of the model.

 It should be noted that this LO is not in the PowerPoint format, but instead is a more extensive set of notes for instructors who are not familiar with the ECW model. It could be condensed and rewritten in the more standard PowerPoint format.

There is also an ECW problem set LO that can used to supplement this LO.

Prerequisites: 
Corequisites: 
Learning Goals: 

After viewing the slides, students, when provided with appropriate data, should be able to:

  • Calculate sigma bond strength in Lewis acid-base adducts using Drago’s ECW model.
  • Show how to deal with any constant energy contribution (W) to the reaction of a particular acid (or base) that is independent of the base (or acid) when an adduct is formed.
  • Garner information regarding steric effects and pi bond stabilization energy in Lewis acid-base adducts using the ECW model.
  • Show using a graphic display of ECW that two parameters for each acid and each base are needed in acid-base models to determine relative strengths of donors and acceptors.
Evaluation
Evaluation Methods: 

This LO has not been used yet and evaluation information will be posted at a later date.

25 Jul 2019

1FLO: One Figure Learning Objects

Submitted by Chip Nataro, Lafayette College
Corequisites: 
9 Jun 2019

An improved method for drawing the bonding MO for dihydrogen

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

When I do this correctly, the students don't accidentally see something which may make immature students giggle.

Evaluation Results: 

I have had multiple colleagues tell me that this technique worked for them and saved them from repeating an embarassing classroom event.

Description: 
Most of us have probably been there. Discussing homonuclear diatomic MO diagrams and on the first day you want to put up the sigma bonding molecular orbital for H2. If you teach it like me, you emphasize the LCAO-MO approach, so you draw a hydrogen atom with its 1s orbital interacting with a hydrogen atom with its 1s orbital...and then you notice giggling from the less mature audience members. My technique will help to prevent this from happening. The technique is in the "faculty only" files section.
Learning Goals: 

The instructor will draw the bonding MO of dihydrogen without accidentally causing laughter in the class or self embarassment.

Corequisites: 
Equipment needs: 

chalkboard or whiteboard

ability to adjust quickly just in case

Prerequisites: 
Implementation Notes: 

I have come close to accidentally drawing the incorrect version of this diagram and I am able to stop myself quickly as illustrated in the instructions. 

Time Required: 
a minute to learn, a lifetime to master.
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.

7 Jun 2019

Guideline for drawing chemical structures

Submitted by Bradley Wile, Ohio Northern University
Description: 

This is the set of guidelines provided for authors by Nature Research. A 6-page PDF gives explicit guidance about rendering molecules using chemical drawing software, and a downloable ChemDraw template (.cds) is provided.

Prerequisites: 
Corequisites: 
Related activities: 
Implementation Notes: 

I give this to all of my research students as part of the welcome to the group package.

6 Jun 2019

VSEPR: Flash Review

Submitted by Christopher Durr, Amherst College
Description: 

This presentation is meant to be a review of applying VSEPRup to steric number 6. It's designed to be viewed as a powerpoint and printed out to keep for the student's notebook.

It can be used at multiple levels: as a review immediately after learning VSEPR in general chemistry, or as a refresher before starting upper level inorganic chemistry. The instructor could add text or voice over the slides to add more detail or leave the presentation as is for students.

If you'd like .psd or .pdf files of the drawings in these presentation, please contact me directly.

Prerequisites: 
Corequisites: 
Learning Goals: 

After reviewing this material students should be able to:

Draw the correct VSEPR predicted structure of a molecule based on steric number and lone pair count.

Name VSEPR structures with their appropriate geometry.

Avoid common VSEPR mistakes, particularly those with steric number 5 and 6.

Recognize how lone pairs distort bond angles from ideal geometry in molecules like ClF3

 

Implementation Notes: 

I plan on uploading this flash review (along with others) to my class site before students arrive to my upper level inorganic course. I will voice over the slides, explaining the concepts, so they're ready to apply molecular orbital theory on the first day of class.

Time Required: 
10 - 15 Minutes
Evaluation
Evaluation Methods: 

I will compare student preparedness between this class and a previous one that did not receive a review.

Evaluation Results: 

This will be updated in the future.

6 Jun 2019

Molecular Orbital Theory: Flash Review

Submitted by Christopher Durr, Amherst College
Description: 

This presentation is meant to be a review of constructing and utilizing an MO diagram, in this case O2. It's designed to be viewed as a powerpoint and printed out to keep for the student's notebook.

It can be used at multiple levels: as a review immediately after learning MO theory in general chemistry, or as a refresher before starting upper level inorganic chemistry. The instructure could add text or voice over the slides to add more detail or leave the presentation as is for students.

If you'd like .psd or .pdf files of the drawings in these presentation, please contact me directly.

 

 

Prerequisites: 
Corequisites: 
Learning Goals: 

After reviewing this material students should be able to:

Recall the shape, size and appropriate nodes of atomic orbitals.

Note the appropriate electron configuration of a given atom.

Draw molecular orbitals with the appropriate sign and node position.

Apply the Aufbau Principle to molecular orbitals to determine the ultimate spin state of a molecule.

Determine the bond order of a molecule from a completed MO diagram.

Manipulate the bond order of a molecule with Reduction/Oxidation.

 

Implementation Notes: 

I plan on uploading this flash review (along with others) to my class site before students arrive to my upper level inorganic course. I will voice over the slides, explaining the concepts, so they're ready to apply molecular orbital theory on the first day of class.

Time Required: 
10 - 15 Minutes
Evaluation
Evaluation Methods: 

I will compare student preparedness between this class and a previous one that did not receive a review.

Evaluation Results: 

This will be updated in the future.

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.
6 Jun 2019
Evaluation Methods: 

The classroom discussion (participation, answers, etc) may be assessed by the instructor, or alternatively, these questions could be given to students to turn in.

Evaluation Results: 

None yet available.  Please leave yours in the comments!

Description: 

This literature discussion aims to have students in an advanced inorganic chemistry course interpret reaction schemes and electronic spectra, relate chemical formulae to molecular structure, and gain an understanding of how inorganic synthesis is planned and executed.  Students should gain an understanding of how counterions and crown ethers affect structure. Question 7 may be expanded to ask students to why pi-donor ability affects ligand field splitting, or as an introfuction to this topic.

An associated 1FLO based on this paper is linked in the related content.

 

Corequisites: 
Course Level: 
Learning Goals: 
Students will be able to:
  • Interpret reaction schemes and write balanced equations.
  • Rationalize the position of a ligand in the spectrochemical series based upon its π-donor/acceptor properties
  • Relate the electronic structure of tetrahedral d8 complexes to their magnetic properties
  • Analyze the impact of countercations on the geometry and electronic properties of the complexes.
Implementation Notes: 

This LO is intended for an advanced inorganic chemistry course.  Students should read the communication before class with questions above as guidance.  A classroom discussion should insue, in which students gain an insight into inorganic synthesis, and recognize how minor differences between compounds, such as counterions, have significant effects on electronic structure.

 

Time Required: 
50 minutes

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