Alpha particles mostly passed through gold foil but some deflected sharply, revealing a small dense positive nucleus.
Practise Atomic Structure & Periodicity All Atomic Structure & Periodicity topics
In 1909 Hans Geiger and Ernest Marsden, working under Ernest Rutherford, fired alpha particles at a thin sheet of gold foil. Most particles passed straight through, a few were deflected through large angles, and roughly 1 in 8000 bounced back. Rutherford concluded that the positive charge and nearly all the mass are concentrated in a nucleus about 10^-15 m across, far smaller than the atom, which is about 10^-10 m across. Electrons occupy the much larger volume around it, so the atom is mostly empty space. The result overturned the plum pudding model.
Key ideas: Alpha particles (He 2+) hit a gold foil about 100 nm thick (Geiger and Marsden, 1909-1911). Roughly 1 in 8000 was deflected through more than 90 degrees and most passed straight through. The nuclear radius is about 10^-15 m against atomic radius of 10^-10 m, a ratio of about 1 to 100000.
Common mistakes and connections: Students explain deflection by electrons, but electrons are far too light to deflect alpha particles; the deflection comes from the heavy positive nucleus. Another error is saying the nucleus fills the atom. The experiment gives the nuclear model, and its flaw (accelerating electrons should spiral in) motivates Bohr.
Rutherford scattering falls as 1 over sin^4 of half the angle: most alpha particles pass nearly straight, but a few rebound from a tiny nucleus. The interactive lesson shows this as a live animation or chart.
It is like firing cannonballs at tissue paper and seeing a few bounce straight back off a small, hard core.
Alpha particles mostly passed through gold foil but some deflected sharply, revealing a small dense positive nucleus.
Rutherford's Gold Foil Experiment is a beginner topic in Atomic Structure & Periodicity. It needs no earlier chemistry lessons and is a good starting point.
Study these earlier topics in Atomic Structure & Periodicity first: Proton, Neutron, Thomson's Plum Pudding Model.
The next topics in Atomic Structure & Periodicity are Nuclear Atom Model and Atomic Number.
Yes. The interactive lesson includes a self-check question on Rutherford's Gold Foil Experiment, and the Atomic Structure & Periodicity quiz draws on every topic in this area.
Rutherford's Gold Foil Experiment is topic 17 of 115 in Atomic Structure & Periodicity.