Molecular Geometry and Molecular Polarity
Tammy S. Gummersheimer, Ph.D.
Schenectady County Community College
In this chemistry lab, the structure of several simple molecules will be examined. Students will draw the Lewis structures, then view and manipulate computerized molecular models of the molecules. From the computerized molecular models, students will determine the shape of the molecule, the bond angles, and the molecular polarity.
The goals of this activity are to provide a visual tool a) for understanding basic shapes of molecules, b) to help the students better understand how lone pairs of electrons on a central atom affect the bond angles in a molecule and c) to better understand how molecular geometry plays a role in molecular polarity.
Context for Use
This laboratory activity is intended for General Chemistry. This activity can be completed in three hours and the only tools necessary are computers equipped with an internet browser, preferably Internet Explorer. Students should be able to draw Lewis structures, determine if individual bonds in a molecule are polar or non-polar, and have been introduced to molecular geometry and molecular polarity before completing this activity.
Description and Teaching Materials
Models 360 is a free collection of 3D Jmol structures used to complete the activity. This is accessible at http://www.chemeddl.org/resources/models360/models.php
The attached student lab/worksheet is also available as a word document on the ChemEd DL's Moodle course at: http://moodle.chemeddl.org/course/view.php?id=78
Teaching Notes and Tips
It is useful to ask students to describe what they are looking at and what it means such that you can clear up any misconceptions they have regarding the models. Its important to make sure the students are visualizing the models in a way that helps them understand the concepts presented in the activity.
By talking to the students during the activity, you can assess whether or not they are utilizing the models in the way the activity intends. The assessment should also include grading the open ended questions to see if the student understands the concept enough to explain it. Additionally, questions on a future quiz or exam will allow you to assess the level of understanding of each of these concepts studied in the activity.
References and Resources
Students view 3D Jmol structures of molecules from the ChemEd DL's resource Models 360 available online for free at: http://www.chemeddl.org/resources/models360/models.php
The student lab/worksheet is available as a word document on the ChemEd DL's Summit Resource Moodle course at: http://moodle.chemeddl.org/course/view.php?id=78
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) 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.
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