Describe Rutherford's alpha particle scattering experiment with a labelled diagram. What did it show, and what were the limits of the nuclear model?

1. 1 · State the aim in one line. To find how positive charge and mass are arranged inside an atom.
2. 2 · Describe the set-up. Alpha particles from a source in a lead block pass through slits and fall on a thin gold foil. A rotating ZnS screen with a microscope counts flashes at each angle. Everything is in vacuum.
3. 3 · Draw the apparatus. [Diagram: source in lead block, slit, beam, gold foil, ZnS screen and microscope on a circular scale, evacuated chamber]
4. 4 · Give the observations. Most pass straight through; a few turn through large angles; about 1 in 8000 bounce back through more than 90°.
5. 5 · State the conclusions. The atom is mostly empty; all positive charge and most mass are in a tiny nucleus (about 10⁻¹⁵ m); electrons revolve round it.
6. 6 · State the two limits. A revolving electron should radiate and spiral in, so the atom would collapse; the model predicts a continuous spectrum, but atoms give line spectra.
7. 7 · Close in one line. So, the experiment discovered the nucleus, but a new idea (Bohr's) was needed to explain stability.

Scoring tip: Draw the diagram first and label every part; labels carry marks. Write each observation next to the conclusion it gives.