Question

Why is Dalton credited with proposing the first atomic theory if Democritus was talking about atoms almost 2,200 years earlier?

Answer 1

I just had this question and I got it wrong but here's what is says to put:  Democritus' ideas were not supported by evidence. Dalton's theory was the first scientific theory because it relied on scientific investigative processes. Dalton's theory was supported by evidence and repeated investigation. 

Answer 2

Democritus *suggested* the existence of the atom, that everything was made up of tiny particles, but wasn't really able to get more specific than that. Dalton also theorized that everything was made up of indivisible particles, but went further basing his theory on actual scientific principles, such as the Law of Conservation of Mass and the Law of Constant Composition. He also said that atoms weren't created or destroyed in a chemical reaction, just rearranged.  There's more to it than that, but basically, Dalton's theory was based more on science while Democritus' theory was too general to be useful in chemical situations.