jan 1, 1904 - 1904
Rutherford discovers that alpha rays are heavy positively charged particles. In 1908, he is awarded a Nobel Prize in Chemistry for his work.
J. J. Thomson proposes the "plum-pudding" model of the atom. In it the atom is envisioned as electrons surrounded by a soup of positive charge, like plums surrounded by pudding.
Added to timeline:
atomic and nuclear physics