Field of Science

Building Skills

video
Grasping the abstract models chemists use to understand what holds a molecule together — its bonding —  is one of the major goals of the general chemistry course I am teaching this semester.   Understanding the bonding in a molecule is the key to predicting and understanding its structure and reactivity.  The models chemists use to describe bonding in molecules range from what can be done on the back on an envelope, such as  Lewis dot structures or VSEPR structures, and those that require hefty amounts of computer time to set up and solve (ab initio MO theory).  The text we are using includes many full color diagrams of bonds, but student still struggle with how these two dimensional representations "work" in three dimensions.

Ad hoc models — mock ups of molecules built by hand from mundane materials such as cardboard and wire — have a venerable history in chemistry.  Watson and Crick used cutouts of the bases to figure out how they paired along the helix; Smalley built a paper model of pentagons and hexagons to see how C60 could be constructed.

So last week, I brought paper, tape and some simple molecular models (tubes and small metal centers which I buy by the bag to hand out to students) to class and asked students to build a valence bond model for acetaldehyde (implicated in hangovers - acetaldehyde, not valence bond theory, though the latter certainly can make students queasy).  Students cut, paste, built and discussed, producing what you see in the slideshow.


With thanks to Danqui Luo, Tess McCabe, Kai Wang, Ben Kaufmann and all the students of Chem 103 who built and photographed the models.

4 comments:

  1. Models are awesome. I've had a blog post on my favourite kit half-finished for months now - this may push me into finally finishing it.

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    1. An essay on models is starting to hatch, I think...they are cool and there is something about building them in ways that you can touch that is particularly cool

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  2. Wow - these are incredible. My high school students don't get that far into orbital theory The curriculum is a kilometer wide and 2.5 cm deep. I am happy if they have a clear understanding that models describing the behavior of submicroscopic particles can be used to understand macroscopic observations. That understanding and the fact that matter is mostly empty space and the requirements on atoms and molecules are done.

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    1. They built some beautiful things, but the best part was watching them figure out how it works.

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