How did Gold foil experiment redefine atomic theory?

The Gold foil experiment redefined atomic theory by proving that atoms have a small, dense, positively charged nucleus.

Ernest Rutherford's Gold foil experiment, conducted in 1911, was a landmark in the development of atomic theory. It fundamentally changed our understanding of the atom's structure, leading to the nuclear model of the atom. Before this experiment, the prevailing model was J.J. Thomson's 'plum pudding' model, which suggested that atoms were a uniform sphere of positive charge with negatively charged electrons embedded within.

Rutherford's experiment involved firing alpha particles (helium nuclei) at a thin sheet of gold foil. According to the 'plum pudding' model, the alpha particles should have passed straight through the foil with minimal deflection. However, Rutherford observed that while most particles did pass straight through, a small number were deflected at large angles, and some even bounced back.

This observation could not be explained by the 'plum pudding' model. Rutherford concluded that the atom must have a small, dense, positively charged nucleus that the alpha particles were colliding with or passing close to, causing them to be deflected. The fact that most particles passed straight through suggested that the rest of the atom was mostly empty space.

This experiment led to the development of the nuclear model of the atom, where the atom is mostly empty space with a small, dense nucleus at the centre, surrounded by a cloud of electrons. This model is still the basis of our understanding of atomic structure today.

In conclusion, the Gold foil experiment was a pivotal moment in the history of atomic theory. It disproved the 'plum pudding' model and led to the development of the nuclear model of the atom, fundamentally changing our understanding of the atom's structure.