Brick, Beaker, Balloon

I’ve been pondering ways to make explicit the macroworld-microworld connections in chemistry, as I’ve been reading Multiple Representations in Chemistry. Chapter 5 on “the role of practical work” discussed the purposes of lab-work and demonstrations in fostering a better understanding of chemistry fundamentals. While many of the examples discussed and the conundrums posed are better aimed at grade-school chemistry and science, there is some overlap to college-level chemistry.

 

An idea that came to mind was to overhaul the approach I’ve used to introduce my chemistry courses. I’ve been starting with the question “What is matter? And why does it matter?” first with the ancient Greek philosophers and the Four Elements, before moving to the alchemists and the philosopher’s stone, and then we discuss Dalton’s Theory and how to picture it, before touching on when we were finally able to “see” atoms with the scanning tunneling microscope. It’s a nice story, but maybe a bit too esoteric and abstract.

 

How can I concretely introduce something we’ll have to do throughout the semester – shift our thoughts facilely between macroscopic and atomistic descriptions, the heart of chemistry. I came up with the 3 B’s. For my first day of class, I can bring in a Brick, a Beaker, and a Balloon.

 

First, I could break the brick. That would be a whole lot more dramatic than what I do now which is tearing paper! Then we can discuss what makes up the brick. Smaller particles? How small? This gets us into the definition of the atom. How are the particles arranged? This gets us into imagining an atomistic picture of solids. What holds the particles together? We can talk about “attractive forces” in general, and how energy is used to overcome those forces and break the brick. It also previews multiple instances in first-semester chemistry where energy will be used to “take things apart” be it knocking electrons off an atom or breaking a chemical bond. We might even discuss the “elements” found in the brick: aluminum, oxygen, silicon. The brick is a compound and not a pure element.

 

Then I could fill the beaker with water. We can imagine what a particle picture would look like, and how this is different from the picture of solids. What’s different? How are the attractive forces different? Why do liquids take the shape of their container? We could discuss the molecular picture of a water molecule and a similar picture when you have many water molecules. But water from the tap isn’t just pure water. There might be dissolved ions. This allows us to talk about homogenous mixtures and maybe what constitutes a “substance”. We could even talk about why pure (deionized) water might be dangerous to their health.

 

Finally, the balloon. We can work on a particle picture of gases and how it differs from solids and liquids. We can think of hot air balloons, and how temperature might change the picture, thus allowing a discussion of the competition between kinetic (thermal) energy and attractive forces between particles. Density enters the picture. We can also talk about the common gases in air, and why balloons that we blow up fall to the ground. I’ve been thinking about how to weave the Gases textbook chapter throughout the semester ever since reading Caesar’s Last Breath, which has lots of great vignettes and examples to keep students curious and interested. While I might not spend as much time on Dalton and his theory, I could at least briefly pay tribute to the fact that his “discoveries” came from the study of gases.

 

I haven’t drawn out a blow-by-blow lesson plan to figure out if all this will fit into a single one-hour session, and how exactly I will use it to leverage other material throughout the semester. But it’s a start. Brick, Beaker, Balloon. It’s macroscopically visual yet full of microscopic imagination. And visual touchpoints make it an accessible and quick reference for students. I’m looking forward to trying it next Fall. Hopefully in front of a live audience!