Tiny atom.
Huge discoveries!

A model is an explanation, not a photograph.

Colors, particle sizes and distances are chosen to help you see the ideas. The nucleus and electrons are enlarged to make them visible: a real nucleus is about 1/100 000 of the atom’s width. Particle sizes are illustrative: they do not represent a mass ratio or actual relative sizes. Motion is illustrative, not a simulation of real electron trajectories. Real atoms are mostly empty space, and electrons do not follow neat planetary paths.

The alpha beam arrives evenly across the atom, as in the real experiment, where the beam was millions of atoms wide. Alphas passing in front of or behind the nucleus are drawn fainter, so a bright path over the nucleus really does pass close to it. Because the nucleus is enlarged, bounce-backs are far more common here than in reality: in Geiger and Marsden’s experiment only about 1 in 8000 alpha particles bounced back. The electron cloud is drawn from hydrogen-like orbitals, a simplification for carbon.

These are simplified classroom versions of historical models. Each view uses six electrons for comparison; the Bohr view shows a carbon arrangement (2, 4). Rutherford’s nucleus is one positive region. Our Bohr view is a modern classroom adaptation: carbon-12 with six protons and six neutrons. Neutrons were discovered by James Chadwick in 1932, after Bohr’s 1913 model. The neutron discovery ↗