Rutherford Discovers the Atomic Nucleus
Alpha particles fired at gold foil bounce backward, and the plum-pudding atom is thrown out overnight
Quick facts
- Experiment
- Gold foil, alpha particle scattering
- Collaborators
- Hans Geiger, Ernest Marsden
- Institution
- University of Manchester
- Nucleus size
- At least 10,000 times smaller than the atom
What happened
In 1911, Ernest Rutherford, working with Hans Geiger and Ernest Marsden at the University of Manchester, fired alpha particles at a thin sheet of gold foil expecting them to pass through with only slight deflection, as predicted by J.J. Thomson's plum-pudding model, in which negative electrons sat scattered through a diffuse cloud of positive charge. Instead, a small fraction of the alpha particles bounced almost straight back. A Purdue University history page records Rutherford's own astonished reaction to the result: “It was quite the most incredible event that has ever happened to me in my life.” Rutherford concluded that all of the positive charge and essentially all of the mass of the atom is concentrated in an infinitesimally small fraction of the total volume of the atom, which he called the nucleus, with his calculations putting the nucleus at least 10,000 times smaller than the atom itself, meaning the vast majority of the volume of an atom is therefore empty space.
Why it matters
Rutherford's gold foil experiment replaced Thomson's plum-pudding atom with the nuclear model still taught today: a tiny, dense, positively charged nucleus surrounded by mostly empty space in which electrons move. The Linda Hall Library situates the discovery precisely, noting it came in 1911 after Rutherford had moved from McGill University in Montreal to the University of Manchester. Rutherford's nuclear atom gave Niels Bohr the physical structure he would quantize just two years later.
How we know
Rutherford published his nuclear model in the London, Edinburgh and Dublin Philosophical Magazine in 1911, based on the measured scattering angles Geiger and Marsden recorded in their gold foil experiments, results that have since been reproduced many times using the same alpha-particle-scattering method.
Sources
- Purdue University, Department of Chemistry. The Discovery of the Nucleus · Reputable sourcechemed.chem.purdue.edu · The domain "chemed.chem.purdue.edu" is on our Reputable source registry. · Link is live and its text matches the event's key terms (Jul 2026)
- Linda Hall Library, Scientist of the Day. Ernest Rutherford · Reputable sourcelindahall.org · The domain "lindahall.org" is on our Reputable source registry. · Link is live and its text matches the event's key terms (Jul 2026)
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