Bonding models: Discrete molecules

9 Jun 2020

Gold carbonyl complexes

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

the first 3 problems are skill practice. The fourth problem is tough and would lead natrually to an in class discussion of bonding models, and how theories change over time.

Evaluation Results: 

I don't have any, unfortunately. 

Description: 

I've been meaning to write an LO on non-classical metal carbonyl complexes for a long time. This paper describes the synthesis and characterization of a gold carbonyl prepared in superacidic media. The LO asks the students to do some relatively straightforward reduced mass calculations to predict the 13C labeled CO stretch from the unlabeled one, but then asks the students to think about /why/ the Au-CO stretch is /higher/ than that of free CO.

Learning Goals: 

Students will practice using reduced mass calculations to calculate labeled stretching frequencies

Students will practice the Dewar-Chatt-Duncanson model of bonding

Students will use an MO diagram and their understanding of MOs to answer the question as to why the CO stretch in a non-classical carbonyl is higher than that of free CO

 

Equipment needs: 

none

Corequisites: 
Course Level: 
Implementation Notes: 

This is billed as an in-class activity because the fourth question is quite difficult. I assigned it as a challenge homework problem during the COVID semester (Spring 2020) but no one did it as far as I can tell. 

Time Required: 
30 minutes with time for discussion at the end
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
21 Mar 2020

chromium and molybdenum arene complexes (COVID-19 version)

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

i have no idea.... yet! (growth mindset!)

Evaluation Results: 

I will report this later this spring.

Description: 

The synthesis of (arene)Cr(CO)3 and (arene)Mo(CO)3 complexes are fairly standard experiments in the organometallic curriculum. I present here some student data and experimental descriptions of real procedures carried out at Harvey Mudd College over the previous two to three years. The word document has the answers in it so it is posted under "faculty resources" but the raw data (pdf or png form) is presented for those who need data to support their distance learning classrooms in the Spring of 2020. I also include an input file for Mo(benzene)(CO)3 should you desire to use WebMO or Gaussian to carry out some calculations. 

 

there was a minor mistake in the reported integrations for one of the complexes in the original faculty only file; it has been fixed in the v2 version.

Course Level: 
Prerequisites: 
Corequisites: 
Learning Goals: 

Students will interpret provided data to write their own experimental sections for molecules they were unable to prepare in the lab. The guided inquiry part allows students to use data to predict the outcome of a chemical reaction.

Equipment needs: 

be able to view PDF/PNG files

Implementation Notes: 

I have not used this yet but will be using it spring 2020.

Time Required: 
unknown
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

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