American Chemical Society (ACS) Chemistry Test 2025 – 400 Free Practice Questions to Pass the Exam

The Plum Pudding model, proposed by J.J. Thomson, suggested that atoms are composed of a positively charged "soup" with negatively charged electrons embedded within it, much like plums in a pudding. This model was a departure from earlier ideas about atomic structure but eventually faced reevaluation.

Ernest Rutherford conducted his famous gold foil experiment, which significantly challenged the Plum Pudding model. In this experiment, he directed a beam of alpha particles at a thin sheet of gold foil and observed how they scattered. Most of the particles passed straight through, but a small fraction were deflected at large angles, and some even bounced back. This unexpected behavior indicated that atoms consist of a small, dense, positively charged nucleus surrounded by a cloud of electrons, rather than being a diffuse mixture.

Rutherford's findings led to the nuclear model of the atom, fundamentally altering the understanding of atomic structure and proving Thomson's Plum Pudding model to be incorrect. This shift to a new model laid the groundwork for modern atomic theory, illustrating the importance of experimental evidence in scientific consensus.