1909, The Charge and Mass of the Electron

Photo Credit: www.biography.com
Year: 1909
Chemist: Robert Millikan
Contribution: Determined the Charge and Mass of the Electron

By performing a series of oil drop experiments, Robert Millikan was able to establish the mass and charge of an electron.

Charge of an electron: e = 1.602 *10-19 coulomb

Mass of  an electron: m = 9.11 *10-28 grams

As J.J. Thomson suggested, electrons are in fact significantly smaller than the nucleus of the atom, but Millikan was able to calibrate Thomson's idea to the exact figures.

Information Credits: Atomic Structure Timeline, The Franklin Institute