How Did We Discover the Atom? A History and Overview

(Last Updated On: September 16, 2019)
How Did We Discover the Atom?

At some point during your education, you’ve likely talked about the atom. While they may provide a few unpleasant high school chemistry flashbacks, atoms are one of the true building blocks of life as we know it. However, there’s one natural question many think of when it comes to atoms. If an atom is so small, how were we able to discover their existence? 

Here is a brief overview on the history of atoms and how we discovered them.

What Is An Atom?

Without getting overly technical, let’s revisit exactly what an atom is first. An atom is the base unit of all matter, as well as the defining structure that builds up each element. The word atom is derived from the Greek term for indivisible because, at the time, we thought that it was impossible to split an atom and that they were the smallest known thing in the universe. Now, we know that’s not the case at all. Every atom is made of the smaller components protons, neutrons, and electrons, and each of those are composed of smaller particles like quarks.

Further reading: What Are Quarks?

While the discovery of atoms as we know them today is (relatively) recent, the foundations for atomic theory actually go much further back in history. In fact, the initial theory of the atom was first recorded by the Greek scientist and philosopher Democritus, all the way back in 440 B.C. Democritus defined his take on what would later become atomic theory by starting with a stone. As he put it, if you were to divide a stone, it would be two smaller stones. Eventually, if you repeated this process over and over, there would be a stone so small you could no longer divide it. 

Other elements of his theory included:

  • The idea that atoms existed separately from each other.
  • There was an infinite amount.
  • That they combine to create matter (but not to make new atoms). 

Ironically, despite being relatively close, Democritus’s ideas were generally passed over in his time. The prevailing theory in those days was that all matter consisted of fire, air, earth, and water. 

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How Did We Discover the Atom?

English chemist John Dalton.

The concept of atoms as we know it would largely remain dormant for hundreds of years. Then in 1808, Chemist John Dalton discovered an interesting fact as he was studying the various elements. In some cases, elements, like tin and oxygen, could merge into various compounds. However, the proportions of each element in every compound always stayed at small numbers, no matter what. If this was the case, there must have been some sort of smaller base unit for the elements. This would be the basis for the atomic theory that he would present that year. Some of his theories, like atoms being indivisible and the foundation for all matter, would be similar to Democritus.

However, Dalton also added his own observations, like the theory that atoms could not be created or destroyed, or that all atoms in a given element were identical. 

And so with all this in mind, our understanding of the atom would continue to evolve. In 1897, J.J. Thomson discovered that atoms were, in fact, not the smallest you could go in terms of particles. At the time, he was experimenting with cathode rays and electric discharge, and while investigating a mysterious glow, he discovered electrons. Called corpuscles at first, these were 2,000 times smaller than hydrogen, and would earn Thomson the Nobel Prize.

Quiz yourself: Pop Quiz: Chemistry

From there, our knowledge of the atom only grew further and further, from Albert Einstein discovering how to weigh an atom, to learning about the structure of the nucleus, to learning about protons and neutrons, to, in time, learning that an atom could be divided. Fast forward to today, and even as so much of our modern science is built off of the atom, we also are learning more about it all the time. Who knows what we’ll be able to discuss if we revisit this topic a few decades from now. 


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