Molecular Structure and Bonding

5 Jun 2020

s-p Mixing and the Order of MOs in Diatomic Molecules

Submitted by Michelle Personick, Wesleyan University
Description: 

These slides provide an introduction to s-p mixing in diatomic molecular orbital diagrams appropriate for students in a general chemistry course. 

In particular, my students were looking for a tool to help them remember which ordering of orbital energies to use. I've always thought that the Z ≤ 7 order (with s-p mixing) looks like a tree. In office hours, a student pointed out that the "standard" (Z ≥ 8) ordering of molecular orbitals looks like a light bulb. Thus, because "it's only Christmas sometimes," the MO diagram with s-p mixing--which looks like a Christmas tree--is only used in a few cases. Light bulbs are used most of the time, so the MO diagram that looks like a light bulb is used for most diatomics.

Corequisites: 
Prerequisites: 
Course Level: 
Learning Goals: 

A student should be able to determine which ordering of molecular orbitals to use in generating a MO diagram for homonuclear and heteronuclear diatomic molecules with and without s-p mixing.

A student should be able to qualitatively explain (1) why s-p mixing only occurs for some elements and (2) why s-p mixing increases the energy of the 2σ MO relative to the 1π MOs.

Implementation Notes: 

I teach primarily using chalk, with slides as needed, so I actually go back and draw the shapes (in colored chalk) over MO diagrams I've previously drawn on the board. The students are suprised and excited to see the shapes emerge.

 

Time Required: 
15 minutes
Evaluation
Evaluation Methods: 

Student learning is assessed using homework assignments and exams.

Relevant questions on exams are generally along the lines of "rank the [number of unpaired electrons in/bond strength of/bond length of] the following 3 molecules" or "give an example of a molecule [with unpaired electrons/that is diamagnetic/etc.]" Questions are short answer, so a justification and correct MO diagrams are required.

Evaluation Results: 

Students in my course love MO diagrams, and will almost always choose to draw MO diagrams when they have a choice of questions on an exam. They also have a very high rate of successfully answering these questions. 

I build on this enthusiasm to briefly show MO diagrams for a few polyatomic molecules and a transition metal complex later in the course. Students find these a bit scary to look at, but are excited that they can at least somewhat interpret them, which they couldn't do at the beginning of the semester. (I show a MO diagram for water on the first day of the semester and they panic, but remember it later.)

The students like MO diagrams because there's a process to follow. The conceptual understanding of s-p mixing is a bit more challenging.

 

19 May 2020

MO diagram for square planar methane guided inquiry

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

Since this is done in class, it is not graded. Since I correct their mistakes in real time, the final MO diagram is usualy almost perfect.

Evaluation Results: 

Students often want to have the electrons in the LGOs 'ride over' on the non-bonding MO instead of falling down to the lowest energy bonding MO. After pointing it out several times in class, students are generally better at using the aufbau principle.

Description: 

This guided inquiry activity takes students through the process of constructing an MO diagram for square planar methane. LGOs are constructed using a graphical approach. Students are guided through a process that allows them to use their MO diagram to make a claim about chemical properties.

Learning Goals: 

Students will derive the LGOs for methane in the D4h point group.

Students will derive the MO diagram for methane in the D4h point group.

Corequisites: 
Course Level: 
Equipment needs: 

none

Implementation Notes: 

This would come after spending several class periods developing LGOs for polyatomics.

I use this method (though not this detailed worksheet) every year in class. I have students divide up into teams and work together at the chalkboard on molecules like borane, methane, water, SF4, and others. I circulate through the class and correct their diagrams in real time. Then at the end, each team presents their MO diagram and its major features.

Time Required: 
30 minutes
19 May 2020

MO diagram for water guided inquiry

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

Since this is done in class, it is not graded. Since I correct their mistakes in real time, the final MO diagram is usualy almost perfect.

Evaluation Results: 

Students don't know which orbitals to mix to form MOs at first and need guidance.

Students don't really understand the concept of hybrid orbitals within the framework of MO theory until they see a few examples.

 

Description: 

This guided inquiry activity takes the students through the whole process of constructing an MO diagram for water in detail. The LGOs are constructed using my graphical approach (linked below) and hybrid orbital formation is discussed. Along the way, students are given hints on what to think about when constructing an MO diagram.

Learning Goals: 

Students will derive the LGOs for water.

Students will derive the MO diagram for water without sp mixing.

Students will derive the MO diagram for water with sp mixing.

 

Corequisites: 
Course Level: 
Equipment needs: 

none

Implementation Notes: 

This would come after spending several class periods developing LGOs for polyatomics.

I use this method (though not this detailed worksheet) every year in class. I have students divide up into teams and work together at the chalkboard on molecules like borane, methane, water, SF4, and others. I circulate through the class and correct their diagrams in real time. Then at the end, each team presents their MO diagram and its major features.

Time Required: 
30 minutes
15 May 2020

Inorganic Active Learning Lesson Plan Design

Submitted by Meghan Porter, Indiana University
Evaluation Methods: 

I use the rubric provided, combined with the peer review feedback (due to COVID, they did not have the chance to revise after the peer review process).  Students must also upload a key with their activity which allows me to catch any misconceptions or inaccuracies in their understanding of the material.

I assigned points as following:

Assignment/Key: See above rubric

Reflection: Worth 5 points total- while mostly graded on completion, I did want to be sure my students were providing more useful feedback than 1 word answers so I gave them the rubric below. (pretty much everyone got a 5)

Completed Reflection

5

3

1

What did you learn from completing this assignment? (i.e. What do you feel that you gained from completing it?)

What did you learn from completing other students' assignments?

What are your thoughts for improving the active learning lesson plan assignment in future iterations?  You may answer this referring to your specific lesson plan or this actual assignment of creating a lesson plan.

 

Meets all criteria at a high level, all questions are thoughtfully addressed

Meets some criteria, some questions are not addressed or non-thoughtful response provided

Meets few criteria, most questions not addressed or responses do not demonstrate thought

Peer Review: Spring 2020 was my first time doing the peer review, and of course covid definitely changed the way I had planned on completing it.  My plan was to have them exchange activities in class or in recitation, work through them in small groups, then be able to provide feedback.  Instead, they had to complete it online and provide feedback- I gave them the basic rubic, but changed the scores to categories of "exceeds expectations", "meets expectations", and "does not meet expectations".

Evaluation Results: 

I am always blown away by the creativity of my students!  While some students submit more group worksheet activities, I have had plenty come up with games, relays, building/using playdough, etc...

Students usually report that they thought they knew a topic- only to begin making an activity and realize they didn't understand it as well as they thought they did.  However, by the time the submitted their activity, they felt like they gained a much more in-depth understanding.  They also loved getting to complete other students' assignments this semester.  Their feedback indicated that they felt it was a great way to review, but also get some insight into how their peers think differently about topics.

Side note: Personally, I love seeing how many students tell me afterward that they have a newfound respect for professors after trying to make their own activity! :-)

Description: 

I created this activity as a way to get the class involved in creating new, fun ways to teach course concepts (selfishly- that part is for me) and for students to review concepts prior to the final exam (for them).  Students use a template to create a 15-20 min activity that can be used in groups during class to teach a concept we have learned during the semester.  We then randomly assign the activities and students work in groups to complete them and provide feedback.

The benefits are twofold:

1. My class is about 100-150 students per semester.  This means that each semester I have a large number of new activities (that I didn't have to make!) to use as a starting point in future semesters as I work to create a more active classroom.

2. The students get a review of the topic they have chosen for their activity, plus, they get to review additional topics from completing and providing feedback on two activities from their peers.

I have run this assignment for three semesters now.  It has been a favorite of my students since the beginning!  I have received a number of activities that I now use in class to teach topics!

Learning Goals: 

A student should be able to

  • Create a lesson plan on an inorganic topic that incorporates active learning
  • Demonstrate understanding of chosen topic via an accurate lesson plan key
  • Review multiple inorganic topics through completion of lesson plans from classmates
  • Provide constructive feedback on classmates’ completed lesson plans

 

Equipment needs: 

None

Corequisites: 
Prerequisites: 
Implementation Notes: 

Since this can be used for any level or any topic, there are plenty of variations you can try!  Some things to consider:

1. You can allow students to select any topic from the entire semester for their activity- this can be helpful prior to a final exam when you want a comprehensive review.  You can also restrict topics if you have areas that you feel your students need to focus on or if you want to assign this before a specific exam.  One of my students also suggested having a sign up sheet for topics on a first-come, first-served basis so that you don't end up with 20 balancing redox reactions and zero crystal field splitting.

2. I have tried students designing plans individually and also working in partners to create acitivties (both outside of class).  Both methods worked well, but in a class of 150, that many individual submissions to grade was a bit overwhelming!

3. The peer review was new this semester (based on a previous student suggestion).  My original plan was have them use a recitation section to work in groups through randomly assgined activities.  Due to COVID, they completed the activites on their own- they enjoyed it, but the group experience would ave been more fun.

4. Depending on your timing, you could have them go through the peer review process and then give them a chance to revise the activity based on the feedback prior to you grading it.

5. The student reflection questions are given as a survey on Canvas after they have completed both the lesson plan and the peer review process.

21 Mar 2020

Ferrocene acylation - The Covid-19 Version

Submitted by Chip Nataro, Lafayette College
Description: 

This is the classic Chromatography of Ferrocene Derivatives experiment from "Synthesis and Technique in Inorganic Chemistry" 3rd Ed. (1986 pp 157-168) by R. J. Angelici. There are no significant changes from the experiment published in the book so details will not be provided. What is provided are links to some excellent videos showing the experiment and characterization data for students to work with. For the time being this will be a living document. Currently it has 1H, 13C{1H}, COSY, DEPT, HMBC, HSQC IR, UV-Vis, GC-MS and Cyclic Voltammetry raw data files for all compounds for students to work with. It also includes processed 1H, 13C{1H}, COSY, DEPT, HMBC, HSQC, IR, GC-MS and Cyclic Voltammetry data for all compounds. If anyone has any additional means of characterization they would like to include (say Mossbauer) please feel free to contact the author.

Corequisites: 
Learning Goals: 

A student should get an appreciation for what doing this lab would be like by watching videos. In addition, the student will analyze the data provided and learn about the characterization of ferrocene, acetylferrocene and 1,1'-diacetylferrocene.

Equipment needs: 

Nothing.

The NMR data comes from a Bruker instrument and can be opened with TopSpin, MestReNova and perhaps other programs.

Implementation Notes: 

Like most everyone at this time this is going to be a trial by fire.

19 Mar 2020

Job's Method - The Covid-19 Version

Submitted by Chip Nataro, Lafayette College
Evaluation Methods: 

Students are generally asked to write a full lab report including an abstract, brief introduction, experimental and results/discussion. I will likely not ask them to do that in this virtual lab. However, they will be asked to determine the value for n for the various [Ni(en)x] solutions as well as questions 1 and 2 from Angelici's book. In addition, I typically ask them to do some literature searching questions, but I am not sure if they will have access to SciFinder so I may have to bypass that or provide them the original papers I have them look at. Links to those papers are included.

Evaluation Results: 

I'll use this in a few weeks and see how it goes.

Description: 

This is the classic Job's Method experiment from "Synthesis and Technique in Inorganic Chemistry" 2nd Ed. (1977 or 1986 pp 108-114) by R. J. Angelici. There are slight changes from the experiment published in the book but they just include running solutions with ethylenediamine mole fractions of 0.67 and 0.75, so details will not be provided. What is provided are a series of pictures and videos showing the experiment being performed. Also included are the raw files of the absorbance spectra in EXCEL. It is not perfect but given the situation many of us are facing at the time this is published, it is better than nothing.Note that this lab was updated on 4/4/2020. The previous data was terrible. New solutions using a fresh bottle of ethylenediamine were prepared. The two solutions mentioned previously were also included. The data is much better. The worked up data has also been included in the instructor only files.

My apologies to my coauthors who spent way too much time looking over the original data set and trying to make sense of it. Their thoughts and insight led to this update. My sincere apologies to anyone else that scuffled over the original data.

Prerequisites: 
Corequisites: 
Course Level: 
Learning Goals: 

A student should get an appreciation for what doing this lab would be like by watching videos. In addition, the student will analyze the data provided and determine the species present in solutions containing various mole fractions of ethylenediamine and Ni(II).

Equipment needs: 

Nothing

Implementation Notes: 

Like most everyone at this time this is going to be a trial by fire.

5 Dec 2019

Flipped Class Module - Lewis Structures of Industrially and Environmentally Relevant Molecules

Submitted by Jack F Eichler, University of California, Riverside
Evaluation Methods: 

1) Performance on the pre-lecture online quiz

2) Performance on the in-class activity (clicker scores or hand-graded worksheet)

 

Evaluation Results: 

Students generally score on average 70% or higher on the pre-lecdure quiz, and on average 70% or more of students correctly answer the in-class clicker questions. 

Description: 

This is a flipped classroom activity intended for use in a first semester general chemistry course. Students are expected to have prior knowledge in identifyng the difference between molecular and ionic compounds, understanding the conceptual framework for how covalent bonds form, and how to draw Lewis dot symbols for atoms, and how to determine the number of valence electrons for atoms.



The activity includes:

1) pre-lecture learning videos that guide students through learning how to draw valid Lewis structures, determining how to caculate the formal charge for atoms in molecular compuonds/Lewis structures, and using formal charge to determine which Lewis structure is most stable if multiple Lewis structures are possible for a given molecule;

2) pre-lecture quiz questions; and

3) an in-class activity that requires students to apply their knowledge of chemical bonding in drawing Lewis structures.

Acknowledgement: This material is based upon work supported by the National Science Foundation under Grant No. 1504989. Any opinions, findings, and conclusions or recommendations expressed in this material are those of the author(s) and do not necessarily reflect the views of the National Science Foundation.

Learning Goals: 

Students should be able to:

a) draw Lewis structures of molecular compounds;

b) determine the formal charge of atoms in molecular compounds;

c) use formal charge to predict the most stable Lewis structure.

 

Equipment needs: 

Suggested technology:

1) online test/quiz function in course management system

2) in-class response system (clickers)

Course Level: 
Corequisites: 
Prerequisites: 
Implementation Notes: 

Attached as separate file. 

Time Required: 
50-80 minutes
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: 

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