Please clarify your question! "Contribution to the atom" is a bit vague. Do you mean:

* Who made important contributions to our understanding of the atom?

* If so, we can discuss figures like Democritus, Dalton, Thomson, Rutherford, Bohr, and many others.

* What specific contributions were made to our understanding of the atom?

* This could cover things like the discovery of the electron, the nuclear model, the development of quantum theory, etc.

Let me know what you're interested in, and I can provide a more specific and helpful answer!