Final answer:
Ernest Rutherford discovered the nucleus through his Gold Foil Experiment by observing the deflection of alpha particles. The experiment showed that atoms have a small and dense positive center called the nucleus.
Step-by-step explanation:
Ernest Rutherford discovered the nucleus through his famous Gold Foil Experiment. In this experiment, he bombarded a thin sheet of gold foil with alpha particles, which are positively charged particles emitted by radioactive sources. Rutherford expected the particles to pass through the foil undeflected, similar to bullets passing through a Styrofoam sheet. However, he observed that some alpha particles were deflected at larger angles or even bounced back. From this observation, Rutherford concluded that atoms must have a small and dense positive center called the nucleus, while the negatively charged electrons orbited around it.