Early model of the atom = no nucleus
Rutherford, Geiger and Marsden did an experiment that challenged this model
They fired alpha particles at thin gold foil in a vacuum and recorded where they went after hitting it
Most went straight through but very occasionally some had very large angle scattering
Small angle scattering = explainable by old model (positive charged atoms repel positive alpha particles)
large angle scattering not explained
force between atom and alpha = very large for large scattering - which is when r = very small
it cannot be explained by the Thomson model because either it passes close - not a small enough r or inside (inside the enclosed charge cancels out so small force)
Rutherford’s model does explain this - much smaller - x 10^-15
