Why atoms, anyway? Teaching the origins of the atomic idea

The correct analogy for the mind is not a vessel that needs filling, but wood that needs igniting... it motivates one towards originality and instills the desire for truth.  – Plutarch, De Auditu

There's only one everything  —  They Might be Giants1

I suspect that I am typical of many chemistry teachers in that I begin my university preparation level classes with a discussion of the historical development of the atom beginning with the ancient Greeks. Current Ontario grade 11 chemistry textbooks make a passing reference to this: "Around 400 BCE, early Greek philosophers argued that matter could be subdivided into tiny indivisible particles called atomos (meaning "cannot be cut" or "indivisible")."2 This idea is usually attributed to Democritus and after reading a few scant lines in a textbook, or a short note on the board, this little detail is passed by without further mention, perhaps destined to make an appearance in the multiple choice section of the unit test or final exam.

I think that this approach misses an opportunity to convey to students something fundamental about the nature and development of modern science. Science, especially chemistry, is about change: explaining it, predicting it and controlling it. To make this point, I ask my students why none of them have taken notice of the textbook (or any other convenient object) that has been sitting motionless on the front counter. After allowing time for the perplexed faces to appear, I suggest that the book holds no interest because nothing about it has changed since the class has begun. Changelessness requires no explanation. But if the book suddenly flew up into the air, or began to change colour or burst into flames, our interest would become immediate and intense — scientific inquiry begins with the question of why things change. It is essential to human nature, and the origin of the scientific endeavour, to want to understand and explain change.

The explanation of how change can occur is the original motivation for the atomic idea. To understand this, the story of the atom has to start with Parmenides — another very influential pre-Socratic philosopher who was born about a century before Democritus.3 It is always shocking to my students when I tell them that Parmenides denied the possibility of change altogether. He argued that being was eternal, changeless and indivisible, completely denying the reality of our everyday experiences. His basic argument was that for change to occur, something which exists must cease to be in order to become something else which did not previously exist. But how is it possible for beings to come in and out of existence to and from nothing? Something coming from nothing for the Greeks was a logical impossibility analogous to the spontaneous generation of a rabbit in a top hat. Thus Parmenides concludes that everything is really just one, eternal, indivisible thing; which implies that the perception of change is an illusion.

To bring the point home to my more visual and kinesthetic learners, I proceed to accept the challenge of Parmenides' student Zeno: that is, to walk between two points along the front of the room. Of course, in order to change my position from point A to point B, I must first walk to the midpoint of AB. From there, I must proceed halfway again to the quarterpoint of AB and so on ad infinitum always remaining half the previous distance away from my destination point B. This argument is just as valid for an infinitesimally small position change, from which we must draw the inescapable conclusion that point B will never be reached no matter how close it is to point A thus demonstrating that all motion is impossible. With tongue firmly placed in cheek, I point out to my students that much of their indignation on hearing these arguments stems from the misconception, undoubtedly learned in math class, that a line segment AB consisting of an infinite number of points could ever possibly be drawn in a finite amount of time.

I interpret constructivist pedagogy as entailing not only the making explicit of student preconceptions, but the active seeking and destroying of complacent, rote learning. It is easy to dismiss these arguments as inconsequential mental trickery, but the resolution of the apparent contradiction between the logic of Parmenides and our sensual experiences was the reason for the atomic idea of Leucippus and his student Democritus.5 The appearance of change is explained by the material existence of tiny, indivisible, immutable little bits of Parmenidian being which interact in a void, while still preserving a changeless underlying reality. Reactants form products in chemical reactions but the elements remain the same. This concept of essential constancy underlying change may be the most fundamental principle in modern science — it is reflected in our laws of conservation and the symmetries employed in the standard model of particle physics.6 From the very start of the semester, I challenge my students to not take for granted the ideas presented to them but to always search for the deeper meanings and interconnectedness of concepts — here lies the true joy of academic learning.

A pause for reflection

To conclude this lesson I ask my students to pause a moment to consider the accomplishment of the ancient Greek philosophers. In a classical, pre-scientific, pre-technological, agrarian-based society consisting of what would now be considered small villages and towns, these people were able to hash out the foundations of modern thought. And, miraculously it would seem, they were able to do it without smart boards, document cameras, or the iPad. How many of us will have an original idea that will still be relevant two-and-a-half millennia after our deaths?

Finally, I fear that some of my readers are thinking to themselves how unrealistic it is to even consider presenting this to high school chemistry students. I am not naive enough to believe that my students come away from this class with any kind of firm understanding of these complicated concepts, but neither is that my real goal. It is alarming how pervasive the view of education as nothing more than the utilitarian training of our young to serve as the future instruments of economic growth is in our current media and politics. As teachers trained in a technical field like chemistry, we are not accustomed to seeing our subject in a broader cultural and historical context. The purpose of this lesson is to give my students some glimpse of education as more than just a hurdle on the road to a medical or engineering career — it is to situate science as part of the greater human endeavour to understand ourselves and our world. If we can just light the spark of intellectual curiosity in our young, I have faith that the rest will take care of itself.


  1. https://www.youtube.com/watch?v=vs_D8dC0uwc
  2. Chemistry 11, Nelson Education Ltd, 2011, page 11. See also Chemistry 11, McGraw-Hill Ryerson, 2011, page 10.
  3. Much of pre-Socratic philosophy was concerned with the question of change, so the choice of our starting point has more to do with pedagogy than historiography.
  4. Indeed, all pencil-drawn lines consist of a large, though finite, number of carbon atoms.
  5. W.K.C. Guthrie, A History of Greek Philosophy, Volume II: The Presocratic Tradition from Parmenides to Democritus, Cambridge University Press, 1965, page 507.
  6. Bruce A. Schumm, Deep Down Things, The Johns Hopkins University Press, Baltimore, 2004. I highly recommend this very readable book to anyone wishing to understand the recent discovery of the Higgs boson.