John Dalton, the father of Atomic Theory, made foundational discoveries about the nature of matter that are often downplayed in the way chemistry is taught today. Isaac Newton famously said, “If I have seen further, it is by standing on the shoulders of giants.” I’d argue that no one embodies this idea better than John Dalton, who built upon ancient ideas to give us the core concept that underpins all modern chemistry. The atom.
When I teach the history of the atom, I tell my students that to understand Dalton, we must first meet the ancient Greeks. Over 2,000 years ago, Leucippus and Democritus imagined slicing matter down to its absolute limit. They reasoned that this process must end at some fundamental, indivisible particle: an atomos, or “uncuttable” thing. It was this powerful, ancient idea, lost to time for centuries.
Yes, the idea that matter was made of atoms had been around for centuries, discussed by thinkers from the ancient Greeks to Robert Boyle. However, it wasn’t a testable theory until Antoine Lavoisier established the Law of Conservation of Mass. By proving that the mass in a chemical reaction remains constant, Lavoisier provided the solid foundation John Dalton needed. Dalton used this principle to show how atoms combine, turning an abstract concept into a quantitative science.
Through a series of experiments with elements like tin, iron, and nitrogen, Dalton developed the idea that elements combine in simple, whole-number ratios to form compounds. This led to the Law of Multiple Proportions, which remains a fundamental concept in chemistry today.
This law states that if two elements form more than one compound between them, the ratio of the masses of the second element that combine with a fixed mass of the first element will be a ratio of whole numbers. A key example comes from Dalton’s experiments with two different compounds of tin and oxygen: one a grey powder and one a white powder. He discovered that for the same amount of tin, the white powder always contained exactly twice the amount of oxygen as the grey powder. This simple 1:2 ratio of oxygen was crucial evidence for his atomic theory.
Based on this, Dalton proposed a revolutionary vision of the atom. His model, now known as the Solid Sphere Model, imagined atoms as the ultimate building blocks: tiny, solid, indestructible spheres. He even developed a unique symbolic language for the elements, using intricate circles rather than the letters we use today. However, Dalton had no concept of the complex world within the atom, they were discoveries for future generations. His atom was a simple, featureless circle. It was the first time we had an idea of what the building blocks of our world may be. Dalton’s ideas, however, would not stand the test of time as almost 90 years later, JJ Thompson discovered the electron proving Dalton fundamentally incorrect in her understanding of what atoms actually looked like.
Now, what most upsets me regarding his theory of the structure of the atom being wrong, is that just because it is wrong, does not mean it is not a good model. In fact we still use it almost all the time.
Recently, when I was teaching the history of the atom to my Year 9 students, I explained all of this rich history of John Dalton and his model of the atom and one pupil put his hand straight up in the air.
“Is this why we draw a solid, liquid and a gas a little circles”
He was absolutely correct. Even two centuries later, when we need to visualise the fundamental behaviour of matter, we all still begin with Dalton’s solid sphere.
The goal of a good scientific model isn’t to be a perfect replica, it’s to be usefully incorrect. Of course, an atom isn’t a solid ball. It’s a complex dynamic globule. But when we want to understand the structure of a water molecule, including the fuzzy details of electron clouds and probabilistic determination would just be confusing noise. So, we simplify. We strip the atom down to its most essential form for that purpose: a sphere that can connect to other spheres. This is why Molymod kits are such an interesting teaching tool. The plastic ball isn’t a failed picture of an atom, it’s a successful tool for building molecules because it makes the important information clear by leaving the unnecessary information out.
Being usefully incorrect is something we are all familiar with. The Tube map, for example, is famously wrong as it ignores streets, distances, and geography. But it’s clever because it simplifies reality to show you only what you need: the connections between stations. The simple, solid-sphere model of an atom does the same thing.
It’s tempting to critique Dalton’s model for what it lacked, but its genius lies in what it started. To say, “He was wrong, let’s move on to JJ Thomson,” is to ignore that without Dalton, there would be nowhere to move on to. Every scientist who came after was not disproving him, but climbing higher on the foundation he laid. His work wasn’t the final answer, but it was the moment we finally started asking the right questions.
The true measure of Dalton’s influence is seen not in his own diagrams, but in the work of those who immediately followed him. His core ideas became the essential starting points for others’ breakthroughs. William Hyde Wollaston took Dalton’s concept of the atom as a sphere and created the first real diagrams of chemical structures. Jöns Jacob Berzelius adapted Dalton’s circular symbols into the efficient letter-based system every chemist now uses and Dmitri Mendeleev relied on Dalton’s pioneering work in determining atomic weights to finally discover the hidden pattern in the elements. Each of these giants built their discoveries directly on Dalton’s shoulders.
I thank Dalton for making the teaching of solids, liquids and gases to Year 7 much easier, but that’s not why he’s my favourite scientist. I admire him for embodying the scientific ideal: that the pursuit of knowledge never ends. He was so dedicated to this principle that he left instructions for one final contribution to science to be made after his death. The story that perfectly demonstrates this has nothing to do with atoms, but everything to do with his eyes.
In a final, beautiful irony, Dalton’s theory about his own colour blindness was also wrong. He hypothesised that the world looked different to him because the fluid in his eyes was blue. So devoted was he to evidence that he instructed his doctor to dissect his eyes after he died to prove it. The doctor did exactly that, only to discover the fluid was perfectly clear. Dalton was wrong (again). And so, the man who gave us the French word for colour blindness, daltonisme, failed to solve the mystery of his own vision.
While the original dissection of Dalton’s eye disproved his theory, the true cause of his colour blindness wasn’t discovered over a century later. The mystery was finally solved when, in 1995, researchers conducted a DNA analysis on fragments of his actual eye 150 years after his death.
This modern technique provided a definitive diagnosis. The analysis showed that Dalton had deuteranopia, a form of red-green colour blindness. He was missing the OPN1MW gene, which contains the instructions for making the pigment in the retina’s cone cells that is sensitive to green light.
Without the ability to properly perceive the middle part of the visible spectrum, his brain could not distinguish between green and red hues. The 1995 study, therefore, provided the concrete, evidence-based explanation that Dalton himself had sought, bringing a clear conclusion to his personal scientific inquiry more than a century after his death.
John Dalton’s work embodies the very spirit of scientific inquiry. Though his atomic theory would later be refined, it highlights a fundamental truth: science advances by correcting its own course. Knowing what something isn’t is a critical step toward discovering what it truly is. The story of Dalton’s atom is the story of science itself: a process where we build upon the insights of our predecessors to lay a foundation for those who follow.
inquestion. 