Final answer:
Ancient Greek philosophers Democritus and Leucippus introduced the concept of atoms as the smallest, indivisible units of matter. The Greek word 'atom' means 'indivisible'. Their theories laid the groundwork for our understanding of the atomic world, suggesting that atoms are in perpetual motion and combine to form all observed substances.
Step-by-step explanation:
The ancient Greek philosophers, Democritus and Leucippus, conceptualized the idea of the atom over 2,500 years ago. The term 'atom' originates from the Greek word aтoмov (atomon), which translates to 'indivisible'. They proposed that atoms were the smallest unit of matter, unable to be split into smaller parts, essentially the building blocks of all substances. Though modern science has shown that atoms can indeed be divided into subatomic particles, this fundamental concept introduced by the Greeks highlighted that atoms were perceived as the ultimate, unchangeable constituents of matter, always in motion within the void.
The Greek atomistic theory was a revolutionary idea at the time, suggesting a universe composed not of one single, unchangeable mass, but rather of countless tiny indivisible particles - atoms, surrounded by empty space, constantly moving and combining in various ways to form the diverse materials and objects observed in the world around them.