Rutherford Model
The nuclear model of the atom, in which a tiny dense positive nucleus is surrounded by orbiting electrons in mostly empty space.
Unit
Dimensionless
In depth
Rutherford proposed it in 1911 after Geiger and Marsden observed that a small fraction of alpha particles fired at gold foil were deflected through large angles. The model located the atom's mass and positive charge but could not explain why the orbiting electrons do not spiral into the nucleus while radiating energy.
Examples in the real world
About one alpha particle in 8000 bounced back from the foil — evidence Rutherford likened to a shell rebounding from tissue paper.