When was the idea of the atom first introduced?

Question

wasnt it around 450 B.C..

Some claim Demotricus introduced it, as the "atomos", but I am not certain on reading his works he understood it as the thing we know as the atom. The best dating we can do is that Leucippus in 420 BC used the concept. They both saw the matter as being an indivisible particle of matter. We generally see the atom as that, but knowing it really can be broken apart.

http://scienceworld.wolfram.com/physics/Atom.html

2+2=