Final answer:
Rutherford's Gold Foil Experiment in 1911, where alpha particles were beamed at thin gold foil, led to the discovery that atoms have a dense, positively charged nucleus, contradicting the previous 'plum pudding model'.
Step-by-step explanation:
Rutherford's Gold Foil Experiment
In 1911, Ernest Rutherford, along with Hans Geiger and Ernest Marsden, conducted an experiment that would alter our understanding of the atomic structure. They directed a beam of high-speed, positively charged alpha particles at a very thin piece of gold foil. The unexpected results showed that while most of the particles passed through the foil, indicating that atoms are mostly empty space, a small fraction were deflected at large angles, and some even bounced back. This surprising outcome led to the conclusion that the atom has a dense, positively charged center, which Rutherford named the nucleus. This experiment dispelled the 'plum pudding model' of the atom, which assumed a uniform distribution of positive charge.
Rutherford's findings indicated that the positive charge of an atom is concentrated in a small central nucleus, with the electrons located outside the nucleus. This nucleus contains nearly all of the atom's mass. The discovery revolutionized atomic theory and was a pivotal moment in the field of nuclear physics.