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Rutherford's scattering experiment
Beginner
Alpha particles revealed a tiny dense nucleus.
Geiger and Marsden fired alpha particles at gold foil; most passed straight through but about 1 in 8000 bounced back, showing a tiny, dense, positive nucleus (~10⁻¹⁵ m) in an atom 10⁻¹⁰ m across.
Atoms are mostly empty space.
Backscattering was impossible for a plum pudding atom.
In more detail
In Rutherford's experiment, alpha particles were fired at thin gold foil, and a few were deflected through large angles. This showed that the atom has a small, dense, positively charged nucleus.
Real-world uses
- The experiment led to the nuclear model of the atom.
- Particle scattering is used to probe the structure of matter today.
- Physics students repeat Rutherford's experiment in simulation to see how a small nucleus deflects alpha particles at large angles.
Open the interactive lesson, with simulation and quiz →
Frequently asked questions
Why were most particles not deflected?
Because the atom is mostly empty space, so most alpha particles pass through without close encounters.
Who performed it?
Geiger and Marsden, under the direction of Rutherford, in 1909.
What did the large-angle scattering show?
That positive charge is concentrated in a very small region, since only a dense, compact centre can send alpha particles back.
Related topics in Atomic & Nuclear Physics
Thomson's plum pudding · Rutherford model limits · Bohr model · Bohr's postulates