In this study guide, we will learn how our understanding of the atom has evolved through philosophical debates, experimental discoveries, and revolutionary theories.

🤔 Early Philosophical Concepts of Atoms

About 2500 years ago, early Greek philosophers believed that the universe was a single, big entity. Contrary to the main beliefs at the time, Democritus was the first philosopher that introduced atomos suggesting that indivisible, small objects make up matter.


Democritus’ atomic model.

Image Courtesy of Sutori

He questioned the infinite divisibility of matter. His theory suggested that, eventually the smallest possible piece would be obtained. In other words, the smallest piece of matter would be indivisible and indestructible.

Despite Democritus’ insights, his theory was met with resistance at the time. Aristotle, a prominent philosopher, proposed an alternative view that all matter was composed of four elements: earth, air, fire, and water, which dominated scientific thought for nearly 2000 years. 🌎

💫 The Chemical Revolution

In the 18th-century, chemistry was considered a formal science. During this time, fundamental laws that hinted at the atomic nature of matter were introduced:

We still use these laws today in our chemical calculations!

🎱 Dalton's Atomic Theory (1803)

This theory is sometimes known as billiard ball model, because Dalton’s atoms were ball-shaped. John Dalton's experiments led to the formulation of a few key postulates:

  1. Matter is made up of atoms.
  2. Atoms combine in whole number ratios to form chemical compounds.
    1. This confirmed Proust’s law of definite proportions.
  3. In chemical reactions, atoms are combined, separated, or rearranged, but never created nor destroyed.