University of Colorado
University of Colorado: Ph Et Interactive Simulations: Models of the Hydrogen Atom
How did scientists figure out the structure of atoms without looking at them? Try out different models by shooting light at the atom. Check how the prediction of the model matches the experimental results.
PBS
Pbs: Planck Discovers the Quantum Nature of Energy
PBS offers a short summary of the discovery of the quantum nature of the atom by Max Planck. Easy to follow.