Bonding models: Discrete molecules

6 May 2019
Evaluation Methods: 
  • The instuctor walked around the classroom to help students individually as needed for immediate assessment.
  • At the end of the class period, students submitted their work to Blackboard for grading.
  • Assignments were graded based on accuracy and quality of the drawings.
Evaluation Results: 

Students generally were able to determine the molecular formula and generate connectivity drawings of the displayed 3-D structures, but really struggled with 3-D drawing. Although this was developed for a course with second year students who had completed general chemistry, even older students in the course struggled with this component. However, by the end of class, all students greatly improved in their ability to understand, interpret, and convey 3-D structure. 

Many students were surprised and many jokes were made about this being a chemistry art class. Although some students didn't particularly enjoy drawing, all understood the value and felt like they had learned something useful. At the end of the semester, many students remarked that the chemical drawing section was the most useful or interesting. 

Description: 

This in-class activity was designed for a Chemical Communications course with second-year students. It is the first part of a two-week segment in which students learn how to use Chemdraw (or similar drawing software) to create digital drawings of molecules.

In this activity, students are given a blank worksheet and 5 models of molecules were placed around the classroom. Students interpreted the 3-D models to determine molecular formulas, connectivity, and generate drawings that convey the 3-D elements. Once students completed the worksheet by hand, they generated the whole worksheet using Chemdraw.

Learning Goals: 

Students will be able to:

1.    Write the formula for a molecule based on a 3-D structure.

2.    Draw a molecule based on a 3-D structure.

3.    Convey 3-D structure of a molecule in a drawing.

4.    Translate molecular connectivity to a drawing that conveys 3 dimensions.

5.    Create digital drawings of molecules using Chemdraw or similar chemical drawing software.

Equipment needs: 
  • Molecular model set for the instructor to prepare structures before class.
  • One computer per student with chemical drawing software such as Chemdraw.
Course Level: 
Implementation Notes: 

Prior to the activity, students were given a brief presentation with an introduction to basic Chemdraw elements using the Chemdraw manual and existing tutorials (see links provided). VSEPR was also reviewed.

For the activity, students were given 3-D models of molecules, and the color key for atom identity was written on the board (eg. blue = oxygen, black = carbon...). The activity was conducted in a class of 24 students, in which each student had access to a computer. The entire class period was 1 hour 50 min, but the activity could be shortened if fewer molecules are included.

Before class, the instructor built models of molecules using a molecular model kit. It is helpful to have multiple copies of each molecule, especially for a larger class, but not critical. The molecules used for the acitvity can be seen in the faculty-only key, and were chosen to have a range of 3-D structures, but other molecules could be chosen. For example, a coordination chemistry or upper division course could have 3-D printed models of crystal structures used as the starting point. 

Time Required: 
60 min
12 Feb 2019

Advanced ChemDraw (2019 Community Challenge #2)

Submitted by S. Chantal E. Stieber, Cal Poly Pomona
Evaluation Methods: 

Students were evaluated during class for effort and participation, and the instructor gave immediate tips and feedback. After students submitted the assignment, it was graded for completion and effort.

 

Evaluation Results: 

Students were allowed to turn in the assignment 2 days later and 22/24 students completed the assignment. The most common errors were slight variances in bond angles and missing colors used in the literature figures. Overall, the quality of the submitted work was impressive, especially for second-year students.

Description: 

This in-class activity was designed for a Chemical Communications course with second-year students. It is the second part of a two-week segment in which students learn how to use ChemDraw (or similar drawing software to create digital drawings of molecules).

In this activity, students learn advanced techniques to visualize complex organometallic molecules and reaction schemes using ChemDraw. Students are presented with several images and reaction schemes taken directly from the organometallic literature and are tasked with recreating the images using ChemDraw. This gives students direct exposure to current literature, while learning useful skills in chemical visualization.

Learning Goals: 

Students will be able to:

1.    Convey 3-D structure of a molecule in a drawing.

2.    Recreate molecular drawings found in the literature.

3.    Create digital drawings of molecules using ChemDraw.

4.    Create digital drawings of reaction schemes & cycles.

Equipment needs: 

Computer for each student with ChemDraw installed.

Implementation Notes: 

This was implemented in a 24-student course in the week following an introduction to basic ChemDraw use. Students were shown the techniques in lecture format using the attached Powerpoint presentation. After the presentation, students had access to the slides and could refer to them while completing the activity. 

In-class most students were mostly able to complete the worksheet using the powerpoint slides as a guide. However, the instructor also walked around to give individual tips and instruction. 

The total time for the activity and lecture was 1 hour 50 min, but it could be shortened or assigned for homework.

In the section where students are asked to interpret molecular formulas, this is done ignoring ligand abbreviations, such as R groups or simplifications of chelating ligands. This could be left off, however it was a useful way to introduce students to drawing simplifications they may find in the literature. Most students just interpreted the formula based on what was drawn, and some students looked up the original papers to get a more accurate formula (although this takes much more time). 

 

Time Required: 
60-110 min
31 Jan 2019
Evaluation Methods: 

Students were evaluated informally as I walked around to help the groups as well as during presentations.

Evaluation Results: 

A large majority of the students had no problem making assignments for the simple and intermediate cases.  This outcome is largely a testament to the ease of use of the CBC method.  In fact, students who had no background in inorganic or organometallic chemistry tended to perform a little better because they were less likely to bring in preconceptions about "oxidation state".

Students struggled a bit with the Z-type Ga ligand, which is great because it helped them move forward in understanding the periodic relationship to Al and B.  Students also struggled a bit with the cyclic (alkyl)aminocarbene ligands in the cobalt dimer, since they had not seen those before.

 

Description: 

This in-class group activity extends my original post by providing more examples of varying difficulty for students to assign MLXZ classifications and electron counts to organometallic complexes.  The answers to these are unambiguous within the CBC system, but they provide excellent starting points for conversation with students about bonding formalisms with organometallics.

Learning Goals: 

* Students should be able to use the covalent bond classification method to assign MLXZ classifications to a variety of organometallic complexes.

* Students should be able to defend their assignments using both organic and inorganic views of structure and bonding.

* Students will understand the ambiguities associated with assigning bond orders, valencies, oxidation states, etc., with the hope that their understanding of covalently bonded organometallic systems will become more nuanced.

 

Course Level: 
Corequisites: 
Implementation Notes: 

I split students into groups of 3, as noted in the handout.  Since this was a small class, I used 10 problems (all 7 from this handout and 3 from the earlier activity) and each student presented one answer.  Students took about 25 minutes to work through the problems, and then I had the students present and encouraged questions and challenges to their assignments.  The students brought several interesting insights that deepened their understanding of bonding and the connection between Organic Chemistry (which they have all taken) and Inorganic/Organometallic Chemistry (which most of them have not seen).

 

Time Required: 
45 minutes
31 Jan 2019
Description: 

This set of slides was made for my Organometallics class based on questions about bridging hydrides and specifically the chromium molecule. I decided to make these slides to answer the questions, and do a DFT calc to show the MO's involved in bonding of the hydride. 

 

Corequisites: 
Learning Goals: 

A student will be able to explain bridging hydride bonding

A student will be able to perform electron counting on a chromium comples with a bridging hydride

A student will be able to interepret calculated DFT molecular orbitals. 

Time Required: 
15 min
Evaluation
Evaluation Methods: 

This was provided as supplementary material outside of lecture. 

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