Fundamentals

First-semester general chemistry begins with fundamentals. What is the fundamental unit of matter? The atom – the (philosophically) indivisible particle. Until it was found to be made of smaller parts! The electron, as exemplified by Thomson’s early experiments, became the next fundamental unit – all atoms had them regardless of identity. What are the fundamental properties of the electron? It is negatively charged (1.6 x 10^-19 Coulomb) and has a measurable mass (9.1 x 10^-31 kg).

 

My students take all this information in stride, especially since many of them have had a chemistry course in high school. These fundamentals seem familiar to them, so one of my goals is to convey the surprising bits. What seems familiar to them was actually very surprising to the scientists as they made their discoveries.

 

This last couple of weeks we’ve been discussing the interaction of light and matter. I’ve talked about the surprises in the photoelectric effect and Bohr’s theory of the atom. Wave-particle duality is another of those strange concepts, and my students are having trouble accepting Heisenberg’s Uncertainty Principle. How can we fundamentally not know? Isn’t it presumptuous to say that we cannot know beyond a certain point where things get fuzzy? Won’t a future generation of scientists be able to solve such a conundrum? Maybe we’ll actually figure out the size of an electron – a seemingly fundamental property that is undetermined.

 

Concurrently, I’ve been reading Fundamentals by Nobel-prize-winning physicist Frank Wilczek. The book has ten short chapters with pithy titles that encompass a fundamental. Chapter 4 is titled “There are Very Few Ingredients”. The fundamental properties of the fundamental particles are just three: mass, charge, spin. I haven’t quite got across to the students how to think of these as labels. Because students think they’re familiar with mass (as a mishmash of weight and density), they also think that charge and spin have a similar sort of physicality to them. I haven’t spent the time in class discussing these sorts of fundamental questions.

 

But I have been using my weekly prompts to get the students thinking about fundamentals, though. This week’s prompt: “Chemistry is all about the behavior of electrons in atoms. While we know the mass and charge of an electron, it turns out there are many other things we don't know, for example its size, or where it is located in an atom (Bohr was wrong about the orbits). It's not just that we don't know, but we fundamentally CANNOT know (Heisenberg's Uncertainty Principle). We can only describe electrons in probabilistic terms. What do you think about this "fuzziness" in our knowledge of electron behavior? Is it strange that we know the mass and charge but can't know other things?”

 

As you can guess, we’re having fun talking about orbitals this week. Or maybe I’m the only one having fun discussing the strangeness of orbitals. I’m not completely sold that this topic should be in a G-Chem class, but I’ve always covered it, partly because I’m a quantum chemist, and partly because many students will encounter orbitals again in O-Chem. At least the students are appreciating the strangeness of it all: certainly when we talk about nodes! How does the electron “cross” a node? They sorta teleport. Sorta like what happens when one observes emission spectra. I’ve been using some of my older blog posts to help students think about this. There’s a fuzziness in all those sorta statements.

 

Wilczek’s chapter reminded me about the importance of fields. Chemists typically don’t think or talk much about fields; they get a brief mention when I define an electromagnetic wave but not much else. Wilczek provides a helpful analogy: “Particles are avatars of fields”. He also discusses why one might have many identical copies of fundamental particles such as the photon or electron with a field framework. In describing the weak force, he says it “supplies a kind of cosmic storage battery, allowing for the slow release of cosmic energy”. Taken out of context, these phrases might seem like new-age-y gobbledygook, but when read in context I found it illuminating as a scientist. The other definition I found useful was when he rearranged Einstein’s famous equation to m = E/c² and defines mass in that way.

 

Reading Wilczek also got me thinking about how I can connect the different topics in my G-Chem class into a more coherent story for the students. I already do this in my own understanding, but I’m reminded that the students don’t necessarily see that framework clearly. I started sketching out a topical flow chart (like a mind map) for my classes and I’m making it a point to consciously communicate this framework to the students. I should go finish up the map. Or maybe get students to do it. I could call it a road map of the fundamentals.