The discovery of the neutron

James Chadwick discovered neutrons by firing alpha particles at beryllium, which fired the unknown particles, which knocked atoms into a gas chamber. The gas became ionized and the charge was used to determine that the unknown uncharged particles had relatively the same mass as protons. He dubbed these particles neutrons.

The discovery of the proton

Rutherford used the Gold Foil experiment to conclude that there was a small, dense cluster of positively charged particles he called protons in the center of the atom, which he called the nucleus.

The discovery of the electron

J.J. Thomson discovered the electron using the cathode ray tube.