Question

When did these scientists make their contributions ? The years

Democritus believes that the universe was made of tiny uncuttable particles.

Heisenberg works with the Quantum Theory

Chadwick finds the missing mass of the atoms nucleus

Dalton's believes that atoms of a given element re identical

Answer 1

There may be people, including chemists, who know and/or remember these dates for these people but I'm not one of them. Frankly being able to spit out these dates, in my opinion, has little to do with knowing chemistry. The easy way to get this information is to go to Google, type in each of these names, and read the summary there. The dates will be there as well as a summary of the important contributions these people made to science.