What experiment led to the understanding of the atomic structure as we know it today?

Rutherford's gold foil experiment played a pivotal role in shaping our current understanding of atomic structure. In this experiment, alpha particles were directed at a very thin gold foil. The findings were unexpected; while most alpha particles passed through the foil with little to no deflection, a small fraction were deflected at large angles, and some even bounced back.

This observation led Rutherford to propose a new model of the atom, dramatically different from the previously accepted plum pudding model. He concluded that atoms consist of a small, dense central nucleus that contains most of the atom's mass and is positively charged, surrounded by a cloud of electrons. This model established the foundation for the nuclear model of the atom, which emphasizes the significance of the nucleus and lays the groundwork for later developments in atomic theory.

Other experiments mentioned contribute essential information to atomic theory, but they do not reshape the model in the same fundamental way that Rutherford's gold foil experiment did. For instance, Millikan's oil drop experiment measured the charge of the electron and provided insights into electron properties, while Thomson's cathode ray experiment discovered the electron itself. Bohr's model later refined the understanding of electron arrangement around the nucleus, but it was Rutherford's experiment that first identified the nucleus as a central component