In 400 B.C, Democritus claimed that atoms are the smallest possible form of matter in the universe. They combined together to form everything known, and are not able to be split.
As believed from 300 B.C to 1800, Aristotle declared that there is a total of four elements that everything is composed of.
In 1803, John Dalton claimed that atoms are an invisible to the eye, indestructable substance that make up everything in life. Atoms making up the same substance were identical, and different substances appeared to be different.