Imagine a middle school teacher who wants to teach about atoms. He’s a progressive guy. He thinks a lot about how to engage his students, and this lesson is no different. Instead of giving a lecture on protons, neutrons, and electrons, he’s planning to have students each choose an element from the periodic table. Then they’ll use household materials to build a model of it, showing the arrangement of particles. He clarifies criteria for success–
- accurately represent the number of protons and electrons for a neutral atom,
- represent a number of neutrons for a common isotope,
- show the arrangement of these particles (In this case, that means distributing the protons and neutrons in a central nucleus, and placing the correct number of electrons in concentric energy levels around it.), and
- clearly label their model with key.
On the day that the projects are finished, the lesson seems like a real success. Student models show a range of effort and aesthetics consideration, but some of them are truly beautiful. Even the simplest models are accurate, and a quiz showed students could identify protons, neutrons, and electrons.
I think lessons like this happen all over the country. And in this post, I would like to suggest that they miss something really important–maybe more important than the idea of sub-atomic particles themselves.
What’s an Atom For?
Most of us think of atoms as something real. No chemist that I’ve ever heard of doubts their existence. We’ve even got pictures of them despite how mind-bendingly small they are. And using some crazy, space-age tech even allows us to move individual atoms around. But for most of chemistry’s history, the atom was just an idea. It’s a really important idea. Some, like Richard Feynman, would argue that it is science’s single most important. And I tend to agree. But it is still an idea.
What’s the point of teaching people about this idea in the first place? (Please don’t say, “So that students will do well on their standardized exams.”) I would argue that the value of teaching any scientific idea (or theory or model or hypothesis) is so that those who learn it can explain something we observe in the real world. Why else have the idea in the first place? The reason, I think, that Feynman and others claim that the idea of the atom is science’s most important, is because it has the greatest power to explain what happens in the world.
I think this is a critical point, and it is one that we often forget. And when we forget it, we start teaching the idea of the atom as an end in itself. On the other hand, if we really stay mindful that the point of the idea is that we can use it to explain things, sooner or later we begin to ask, “What are they going to explain?”
Using the Idea
When I taught middle school, the things that my colleagues and I hoped our students would be able to explain by the end of eighth grade included:
- Why are some things solid, when others aren’t?
- Why does water boil at 100 degrees and no other temperature?
- Why does butter melt at a completely different temperature than chocolate?
- If the table is just made of atoms, why can’t I brush them or rub them away?
- Is air something real, like, does it weigh something?
- Can something be truly empty?
- How could the air in my tire hold my car off the ground when I can’t lift it at all?
The idea that atoms are constantly moving, take up space, have mass, and (depending on the type) are attracted to each other can explain all of these and a lot more.
For nearly all of the nineteenth century, the idea of the atom was hardly more sophisticated than that. Chemists didn’t know (or need to know) about electrons to use their atomic model to answer any of the questions above. Middle school students don’t need anything more sophisticated either. What they do need is time and practice using the model–trying to make sense of puzzling events by thinking about the world in terms of its tiny pieces. Time spent memorizing details about sub-atomic particles detracts from time for that all-important task.
The Evolution of the Atom
It’s customary, at the beginning of many high school textbooks, to discuss the development of the atomic model. This development is usually shown in a linear progression where each new idea is named after a scientist important in its discovery: Dalton, Thompson, Rutherford, Bohr. And all the way at the end is the current model, the electron cloud. It reminds me of the other misleading picture from biology showing the march of human ancestry as a line of shambling apes who, on a singular trajectory, gradually and inevitably become more human. The atomic model progression is just as misleading–making it seem as if the march toward the electron cloud idea was tidy and progressive and inevitable. It gives the sense that the electron cloud model is the end, that no more models exist.
The funny thing is that lots of high school chemistry doesn’t make use of the electron cloud model at all. There is no need for it! Chemistry is complicated stuff, and many students will spend lots of time just understanding how electrons can “orbit” the atom in different “energy levels” and how that affects which atoms can bond with whom. This is perfectly good chemistry, and our students are not being short-changed if that is where they spend most of their time. But its worth pointing out that they can do all of this work with the Bohr model–not the electron cloud.
Chemists use the Bohr model all the time because it is useful–even if it isn’t the most perfect model that we have. In the same way, physicists use Newton’s Law of Gravitation even though, technically, it’s been superseded by Einstein’s ideas about relativity.
Why not use the most up-to-date models or theories all the time? Well, mostly because they are complicated, abstract, hard to visualize, and difficult to use. We invented them because we eventually came upon phenomena in the world that our old models just couldn’t explain. But unless we’re dealing with those weird circumstances, we don’t need them, and we naturally and rightly return to the simplest means at our disposal.
The Dalton Model
I would propose that most student in middle school needn’t learn about electrons, protons, and neutrons at all.
I know this is an idea that many science teachers will find unsettling. But if we are to treat seriously the idea that scientific ideas are good when they are useful, I don’t see how the ideas of protons, neutrons, and electrons can pass the test for middle schoolers. Electrons may explain to an high school student why carbon will bond with four hydrogen atoms to form methane but won’t bond with just one or two. But to middle school students who are just tentatively beginning to think about what a chemical reaction is at all, the niceties of how bonds form will cloud explanations rather than elucidate them. Instead, let’s let students become fluent with the atomic model first. There will be plenty of time to throw complications at them later.
In this way, the mental journey that students take through chemistry will mirror that taken by the scientific community as a whole. During the long century when scientists got to play with the atomic model in its simplest form, atoms were imagined as little balls. A lot was discovered about how the world worked with this Dalton model. Let’s give our students the same luxury.
Are we Lying
“But,” I can hear people say, “What’s wrong with teaching middle schoolers about electrons, protons, and neutrons? It’s not going to hurt them. Besides, they like learning about them. And even if they don’t need them as part of their mental tool kit now, they will need them eventually. Are we really supposed to withhold more accurate information from them just because they don’t have a practical purpose for it yet?”
And I agree with nearly all of this. Middle schoolers are totally capable of learning and understanding, in basic form, what subatomic particles are. And it doesn’t hurt them learn these ideas early. Where I differ is in thinking of the more complex model as more accurate. When we start to think of one of our models as being “the right answer,” we forget that all of our models are inaccurate. All of them are simplifications of a real world that is too wild, too baroque, too dizzylingly big (and small) for us to comprehend.
Maybe one of the biggest dangers of giving students a complicated, fully-fleshed out model before they can use them is the illusion that someone has got all of this mystery figured out already. It makes the process of discovery invisible.
What we Gain from this Approach
First, by cutting away the details, students will have more time to put the model to use. We can challenge them to use the model to explain why water beads up in spherical droplets or why burning alcohol seems to disappear. This gives them first-hand experience in how models in science are actually used.
Second, I think the greatest advantage that we get from waiting is this–eventually the model that they’ve worked with for months (or even years) will come up against phenomena it can’t explain. Why does a wire conduct electricity? Why does uranium appear to decay into lead? Why doesn’t helium seem to react with anything at all?
When this happens, probably in the early years of high school, students will have to wrestle the same way J. J. Thomson did in 1897 when he was playing with a cathode ray tube and noticed that he could bend a beam of “cathode rays” with a magnet. Thomson current model of the atom couldn’t explain that.
So he changed it.
And students, when they finally come up against questions like this, will have to as well. It will confuse them. It will involve them in argument. They’ll probably go down several wrong paths before they arrive at something satisfying. But in the process, they will feel in their bones that tension between trust in scientific ideas and an acknowledgement of their limits–something that is so devilishly hard, and so critically important, for non-scientists to understand. They will know, deeply, how a theory can be something that remains revisable and still inspires tremendous confidence. They will get a sense of the beauty of a human endeavor that acknowledges our human foibles and is designed to correct itself. And they will, perhaps, get a sense of how science helps us all to become progressively less wrong.