Atom Models

Around 400 BC, the Greek philosophers Leucippus and Democritus first proposed that matter, if repeatedly subdivided, would eventually yield indivisible atoms. Centuries later, once experimental physics and chemistry matured, scientists needed a concrete physical model of what an atom actually looks like on the inside, in order to explain the measured properties of bulk matter.

J.J. Thomson proposed the first quantitative theoretical model, based on a static distribution of electric charge - but this model could not explain why atoms are stable. His own student, Ernest Rutherford, then proposed the first dynamic model, grounded in the results of the gold-foil alpha-scattering experiment carried out by his students Geiger and Marsden - but this model, too, ultimately failed to explain atomic stability. Finally, Niels Bohr, himself a student of Rutherford, proposed a model of the hydrogen atom that succeeded where the others failed: it explained both the atom's stability and the discrete line spectrum that hydrogen is observed to emit. …