Who discovered the electron?

J. J. Thomson discovered the electron. In 1897, while studying cathode rays, the British physicist showed that they consisted of negatively charged particles far smaller than atoms.

Thomson compared how cathode rays were deflected by electric and magnetic fields. The resulting charge-to-mass measurements indicated that the particles were over a thousand times lighter than a hydrogen atom. Because the result did not depend on the material used in the apparatus, he argued that these particles were universal components of matter.

Thomson initially called them “corpuscles”; the name electron, proposed earlier by George Johnstone Stoney, later became standard. His discovery demonstrated that atoms were divisible, overturning the older idea that atoms were the smallest indivisible units.

Thomson later proposed the plum pudding model, picturing electrons embedded in diffuse positive charge. Ernest Rutherford's gold-foil experiments replaced that model with the nuclear atom. Thomson won the 1906 Nobel Prize in Physics, not Chemistry, for his investigations of electricity conducted through gases.