Monday, July 23, 2012

#ModChem Day 9: Part 2 - Development of Subatomic Particles

Modeler's Log, Day 9--

After we finished with our thought-provoking whiteboarding session and article discussion, which you can read about in detail here, we continued through the historical development of the atomic model to the existence of a subatomic particle that has negative charge. This was accomplished using explorations into the work of Faraday, Crooks and Thomson.

We conducted (heheh..."conducted") the sticky tape lab where we tested the attraction and repulsion of Scotch tape strips to different materials, which led us to arrive at a need for particles smaller than an atom; moreover, the conclusion that a negatively charged particle (later called an electron) must exist inside of the atom! The "Sticky Tape Lab" (which can be found in its full modeling entirety on the AMTA website) is a rework of a classic physics electrostatics lab. This lab provided students an opportunity to test the behavior of strips of tape, which had been ripped apart from each other, when in brought in proximity to aluminum, paper, glass, and other ripped apart strips of tape.
We generated three possible expected outcomes during the design and setup of the lab, including that materials would attract, repel, or do nothing. After testing all the materials against each other, we constructed a matrix that displayed the results:

Based on our results, we determined the charge of each piece of the tape and thus the charge on the other materials as well. Following a very informative video about cathode rays and the experiments surrounding them, the model development to arrive at the existence of charged subatomic particles was complex but happened--this will take carefully crafted planning to do with students, but was really impressive because of how it followed a similar development of the charge model in physics.

Our model developed to accommodate the transfer and flow of charged particles, as well as help us to characterize our newly "discovered" charged particle. We were able to represent charged particles inside of the atom in a primitive way along with introduce a new property: conductivity! As it turns out, the model we arrived at was that of J.J. Thomson's "plum pudding," but it explained all that we had seen quite well. In context with what we have been doing all year, it makes sense to arrive at this model of the atom at this time; however, there was copious discontent with even exploring this model much more than out of honorable mention considering what we currently know about atomic theory.

It's important to note here that the atomic models developed throughout history are NOT merely artifacts but rather evidence-based and well-reasoned attempts to explain the science behind matter and its interactions. All too often, the "history of the atom" chapter is glossed over in chemistry classes by students, because it has the word "history" in it, and by teachers who rush through it to get to the "true (current) stuff" about the atom. I have to admit that I used to be one of those teachers; however, I was never given a full understanding of the development of the atomic model and now I have a MUCH greater appreciation for it and see how important it is in understanding chemistry. Though it may seem unnatural to follow chemistry through a chronological progression of atomic model development, we cannot reduce the model development to mere prestidigitation and page turning in a textbook. This methodology doesn't just honor the "history of the atom," it simulates the models of the atom historically and in context with the associated chemistry that was known at all the points along the way. Resist the urge at this point in the curriculum to jump to a "full-blown" model of the atom that uses all the common jargon, even if it is true that students "already know" that atoms have these subatomic particles. Stick with plum pudding and let the rest come in time.

As a final aside, I always wondered who ever liked plum pudding anyway, I never remember Bill Cosby advertising it! Then again, I shouldn't knock it before I try it. Perhaps we'll just have to make some plum pudding this year in chemistry and taste it for ourselves! That'd be memorable, right?!

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