Ernest Rutherford was the first to uncover the structure of the atom in the 1910s.
Rutherford’s breakthrough came from the Geiger–Marsden, or gold-foil, experiment conducted in 1909. Alpha particles were fired at a very thin sheet of gold. Most passed straight through, but a small number were deflected sharply, including a few that bounced almost backward.
In 1911, Rutherford explained the results with a new atomic model. He proposed that nearly all an atom’s positive charge and mass are concentrated in a tiny, dense nucleus, while the rest of the atom is mostly empty space. This overturned the earlier “plum pudding” model associated with J. J. Thomson.
Rutherford did not discover every component of the atom. His work established the nuclear structure, while later scientists identified and clarified particles such as the neutron and developed quantum models. He also demonstrated the existence of the atomic nucleus and later helped identify the proton, making his work foundational to modern nuclear physics.