When was the atomic discovered?

Answer 1

Leucippus is a mysterious figure whose exact dates are unknown - some say he never existed - but is still considered the be the founder of the Atomistic theory. Democritus was born 460 B.C. and died 370 B.C. He was a disciple of Leucippus and both men are credited with the atomistic theory.

Answer 2

That's a complicated question, with an answer that needs both philosophy and science. There was no single experiment which suddenly showed the existence of atoms. The story starts with the ancient Greeks.

Democritus and Leucippus were philosophers in the 5th century B.C. and they talked about the idea of atoms as fundamental parts of substances, but they were putting forward ways of thinking, they did not perform experiments to test their ideas. Other philosophers, such as Aristotle, disagreed with them, and the idea did not become the accepted way to think. There is evidence that the idea also arose, possibly independently, in India a century later.

It was not until after the renaissance that evidence based science took off and our modern way of looking at it began. Isaac newton speculated on the idea of atoms, but the man credited with establishing the atomic theory properly was John Dalton. Careful work had been done which established that when elements combine they tend to do so in fixed proportions by mass. Dalton reasoned that this was because each element consists of tiny atoms whose masses are fixed and are in the same ratios as the combining masses. This theory became widely accepted and much other evidence was built up to support it.

So, in a sense, atoms were not discovered at all, they were a theory which explained the experimental facts. However it is possible these days to produce electron microscope images which actually show single atoms.