Molecular Modeling of Bond Type, Polarity, and Resonance Using Models 360

This page authored by Darcy Mack, Pasadena City College, based on an activity by Padma Ganapathi, Pasadena City College.
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Summary

In this computer-based lab, students compare a series of compounds (ethane, ethene, ethyne as well as propane, propene, and propyne) in terms of Lewis structure, C-C and C-H bond length, bond angle, type of C-C bond, and hybridization to understand how type of bond affects bond length and bond angle. Then students draw the shapes and net dipoles for various compounds and compare their shapes to the computer generated models and dipole moments. Students will also compare ozone and the carbonate ion in terms of bond length, bond angle, dipole moment, and electrostatic charge to help them better understand resonance. Students will use the free web-based program Models 360 to complete their investigation.

Learning Goals

The major goal is to help students understand how bond type and resonance affect the bond lengths, bond angles, and dipole moments of molecules. Models 360 gives students a chance to visualize these difficult concepts. Also students will gain experience with determining trends from data, data analysis, and critical thinking.

Context for Use

This lab is designed for a class of 30 first semester general chemistry students at a community college. Students need access to computers to complete the lab. Students should already be familiar with Lewis structures, VSEPR theory, and bond order. The lab is designed to take place during one 2-hour lab when paired with the students using traditional ball and stick models to make the shapes of the molecules in part B. Time can be adjusted by letting students complete the Lewis structures and drawings in class or at home as well as adding or removing the traditional ball and stick models. The activity should take between an hour to an hour and a half if completed as written.

Description and Teaching Materials

The activity is included in the Word file. The file includes a link to a webpage that I created which includes the directions to part of the activity and displays the molecules to compare in part A on the same page. The activity can be modified to have the students find the molecules on their own in Models 360 so that they do not need to use the webpage. If the activity is modified in that way, the directions from the webpage need to be added into the Word file of the activity. Student Handout for Molecular Modeling Assignment (Microsoft Word 95kB Jul3 12)




Teaching Notes and Tips

The activity was created so that students could view multiple representations of molecular shapes at once. Thus if students have access to laptops, they can view their own drawing of the molecular shape, the traditional ball-and-stick model, and the computer generated model at the same time. Since Models360 already has the molecule or ion generated in its database based on experimental data, sometimes the computer-generated model's dipole does not match the net dipole moment you would expect based on theory. Thus before adding any other molecule or polyatomic ion to the lab, it may be helpful to check Models360 to make sure that the chemical species is included in the Models360 database and that the dipole matches the predictions so that the students will not be confused. Also, the students may need some extra reinforcement on the topics of resonance to help them answer some of the questions included in the activity.

Assessment

This lab can be assessed like any other lab. The students can perform the tasks individually or in a group depending on what is appropriate for the particular class.

References and Resources

The following resources are also included in the file of the lab itself.
The website http://faculty.pasadena.edu/drmack/classes/Chem_1A_files/SA-MPart1.htm or the shortcut http://goo.gl/4jHpw provide the directions for the activity.

The free web-based program Models360 can be found by clicking on the following website: http://www.chemeddl.org/resources/models360/.

The ChemEd DL Summit Resource Course (http://moodle.chemeddl.org/course/view.php?id=78) houses all of the submissions from two-year and four-year college faculty members who have designed resources using the Chem Ed DL (Chemical Educational Digital Library at http://www.chemeddl.org) for use in organic chemistry and general chemistry classrooms and laboratories.

This resource is based upon work supported by the National Science Foundation under Grants No. NSF-DUE 1044239 and NSF-DUE 0937796. Any opinions, findings, and conclusions or recommendations expressed in this material are those of the author and do not necessarily reflect the views of the National Science Foundation.