In fact, when Democritus raised the existence of atoms he was referring to infinitely small elements that could not be divided, hence his name, atom (which means "indivisible"). Scientists believed they found an element that cannot be divided in the 19th century, and they named it an atom, taking up the ideas of Democritus, but in the following century it was shown that the atom could be subdivided and therefore the original idea of Democritus was rejected. As far as we know Democritus could be wrong, (or maybe not). And atoms have a name that doesn't really fit it, but we still call it that even though we're wrong... we don't really care.