The ancient Greek philosopher Leucippus taught his students to notice that while sand is made of fine particles, from a distance the beach looks continuous like the sea. Thinking along these lines, one of his students, Democritus, came to the conclusion that all matter is ultimately made of indivisible particles. He gave them the name atomon. Remember that when a doctor removes your appendix we call it an appendectomy, and when the tonsils are removed we call the affair a tonsillectomy, the suffix tomy coming from the ancient Greek word for cutting or dividing. Thus atomon means "it can’t be divided," and in time became our word atom.

Little is known about the life of Democritus, who hailed from the city of Abdera in Thrace. We do know that his ideas did not catch on. Rather, Aristotle’s view that matter is continuous and infinitely divisible held sway for more than 2,000 years, until the early 1800s, when John Dalton demonstrated that atoms did a very good job of explaining what was observed in chemical transformations. Even so, not all scientists were convinced that matter was made of atoms until the early 1900s, when The Svedberg’s studies of Brownian motion gave unequivocal proof of their existence.