Ancient Web: Purdue Walked Students from Hydrogen Lines to Bohr Orbits

Part of the Ancient Web Collection.

The little colored lines produced by glowing hydrogen are an invitation to rethink what an atom actually is. One surviving Purdue University tutorial treats those lines as the start of a careful intellectual journey.

Read Development of Current Atomic Theory.

The lesson begins with an experiment: pass light from a low-pressure hydrogen discharge tube through a prism. Instead of a continuous rainbow, four visible spectral lines appear around 656, 486, 434, and 410 nanometers. The author then introduces Planck's energy packets and Einstein's photons as the concepts required to explain why the colors are discrete.

Next comes Niels Bohr. In the tutorial's account, electrons may occupy only certain allowed orbits, and a change between them produces light whose energy equals the difference between the two states. It follows the reasoning through an example: a transition from the fourth to the second level predicts a wavelength close to the observed blue-green hydrogen line.

A model that works—and then fails

The page does not leave Bohr's tidy planetary picture unchallenged. It explains why an electron is not simply a small ball following a classical circular path. Louis de Broglie's wave-particle reasoning leads into electron diffraction, and the closing section introduces Schrödinger's wave functions and probabilistic orbitals.

Worked problems invite visitors to calculate the energy of a red photon and the wavelength associated with an electronic transition. A companion tutorial on quantum numbers extends the subject into subshells and electron configurations. Both sit within a much larger general-chemistry review built from linked lessons.

The original queue URL ends in bohr.html; the readable page is currently served at bohr.php. The page does not establish its exact first-publication date, and its equations may render awkwardly in modern text extraction. It is a surviving university Web courseware chapter, not a time-stamped physics discovery.

Other Ancient Web articles cover Purdue's gold-foil history and its atom-and-ion basics. This one is distinct: it documents an extended explanation of how an elegant but limited atomic model gave way to quantum mechanics.

Follow the complete Bohr-to-Schrödinger lesson.

Part of the Ancient Web Collection.