Physics&Parsimony

About physics and teaching

Chemistry with Rising 9th Graders

with 6 comments

I spent three weeks this summer teaching chemistry to rising ninth graders in an academic program designed for students who are transitioning from public middle schools to independent high schools. Earlier this summer, when I was told that the program director wanted us to teach chemistry, I decided to look into the Chemistry Modeling materials and to read up on what kind of misconceptions high school students harbor about chemistry and atoms. The materials make a very convincing argument that students who lack a solid conception of atoms as building blocks are at a distinct disadvantage in high school chemistry. So I decided to focus the entire three weeks (really only two and a half weeks of class time) on a modified first unit of the Chemistry Modeling materials. This unit focuses on using atoms to describe chemical and physical changes.

I was prepared for the students to not have an atomic model useful for creating explanations. I saw that, indeed, while they all knew gases and liquids and solids are made up of connected atoms, they could not use this fact to describe chemical or physical changes very well. For instance, what is between the nitrogen and oxygen molecules in the room? (Typical answer: air.) I was ready for this.

What surprised me was that almost all of these students knew how to balance chemical equations. Yet they had no idea what any of it meant. They could also tell me that burning alcohol was alcohol reacting with oxygen and the result was water and carbon dioxide (some wanted to add intermediate “fire atoms,” though). While they had been taught to balance a combustion equation and even knew quite a lot about combustion, they nonetheless (to a student) had no idea what was going on.

Wait! If they know that alcohol and oxygen react, and the result is carbon dioxide and water, and they can even balance a chemical equation for the reaction, doesn’t that mean they know what’s going on? Well, using the modeling materials and letting the students talk and discuss and talk some more, you find out some very interesting things. First, the alcohol evaporates when it reacts with oxygen. The oxygen gets “used up” when it reacts with the alcohol. What does it mean “gets used up?” It apparently means that it is gone. Where did the carbon dioxide come from? It was in the air already. And the water? It’s around, too.

Thus, the atoms on the left hand side of the chemical reaction equation are totally different from the atoms on the right side of the equation in the middle school student’s mind. Why do we teach them to balance chemical equations in middle school? I wondered this when my daughter was in middle school, too. Note also, that all of these students were middle school over-achievers.

Also, I found out that molecules are not always seen as collections of atoms. They might even be containers. When sugar dissolves in water, the sugar molecules go inside the water molecules, which carry them around, like so many little kangaroos carrying their babies. Interesting stuff! In fact, if something starts off as a solid (like ground coffee) or a liquid (like perfume) and some of those molecules get into the air (we know because we can smell them), they could only get to our noses by hitching a ride on oxygen molecules. That is, these other molecules are incapable of flying around the room on their own, they have to be carried (always by oxygen, by the way, never by any other gas molecule!).

So the typical misconceptions about the atomic model go far deeper than I ever imagined. I was fascinated by this fact, and I pared back what I had planned and went even slower, giving the students more time to discuss and talk and describe. In the end, I’m not sure we got very far, but I’m pretty sure I gave them plenty to think about. I hope it helps them out in high school!

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Written by Mark Hammond

2011/08/23 at 20:44

Posted in Uncategorized

6 Responses

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  1. Excellent observations! I am teaching 10th and 11th graders and I notice the same thing. I always ask my students “When water is boiling, what is in the bubbles?” Inevitably, their answer is “air”. Teaching the particle model is so much more important at this level, but we need to get the state standards changed to reflect this.

    Michael

    2011/08/23 at 21:21

    • I help write the chemistry (and science) standards for my state and the intention is there that the particle model be understood. In practice, not all students will be at a level of abstract thought where they can fully use a great chemical model, so (our) standards were written so that a student could demonstrate their level of abstract model building, rather than expecting all students to be able to hold a realistic picture of atoms and molecules in their heads. Our intention was to urge the teachers to push that as hard as they can but to not make it a breaking point. Abstract thought comes at different points of time but it can always be part of the effort.

      trickfletcher

      2011/08/24 at 14:46

  2. Nice teaching. I’ll help them with the facts in college – but especially in middle school, help them grow their imaginations. Nice work.

    trickfletcher

    2011/08/23 at 22:41

  3. Thanks for this — I will use some of it in my intro class this September (you mentioned reading up on misconceptions… I’d love to read more about the specifics you found or the resources you used!).

    If you’re not already reading Michael Doyle’s blog, this post about combustion might resonate. Doyle’s got a lovely meditative writing style, too — I swear he can lower your heart rate from across the country. Even when he’s teaching with a flamethrower.

    Mylène

    2011/08/23 at 23:48

  4. I was reading the Chemistry Modeling Instruction teacher notes from ASU. In particular, the second unit (which I did not use in my class) mentions a paper by Vanessa Barker (University of London, in a report “Beyond Appearances: Students’ misconceptions about basic chemical ideas”), and quotes the paper. This is what got me thinking about just narrowing down my goal for the three week session to just concentrate on creating a useful atomic model of matter.

    Mark Hammond

    2011/08/24 at 10:46

  5. Heh, I like the idea of roo pouches for sugar water. Cute =P And fire atoms too! It’s funny how basically Greek perceptions of the elements still seem to be so prevalent though.

    Natalie Hunter

    2011/08/30 at 15:56


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