jan 1, 1897 - J.J. Thomson discovered the electron.
After his discovery of the electron, which are the negatively charged subatomic particles in the atom, it was known that there was more than one subatomic particle in the atom and people started making atomic models to show how the things in the atom were made up. Thomson’s model was called the plum-pudding model where electrons were just stuck into a lump of positive charge. His model was incorrect but pushed his former student to come up with a new discovery and a more accurate model.
Added to timeline:
The Atom vs the Telephone