jan 1, 1904 - Hantaro Nagaoka suggested that the atom had a nucleus.
He proposed that there was a central nucleus in the atom and that electrons “orbit” the nucleus. His thoughts and ideas on the atom went against the plum-pudding model of J.J. Tomson. It provided a gateway for further studies on more advanced models of the atom, specifically done by Ernest Rutherford who proved his theory to be correct in later years. His model set an example for further scientists to experiment with his concept and create more accurate models.
Added to timeline:
The Atom vs the Telephone