Our understanding of atoms dates back to the Greek philosopher Democritus. Around 530 B.C., he wrote that atoms moved about in a void. They bounced off one another or joined together to form clusters.
He believed that all changes in the world came from changes in the movement of atoms or in the way atoms were packed together.
Democritus’s ideas stayed pretty much unchallenged until the nineteenth century. That era marked the beginning of startling discoveries about the atom. And the discoveries continue to this day.