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Hydrogen Atom

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The hydrogen atom — one Proton and one Electron — is the simplest atom and the benchmark against which every model of atomic structure, orthodox or otherwise, is measured.

The standard account

Hydrogen's visible spectrum was fitted empirically by Balmer in 1885 and generalised by Rydberg; the Rydberg constant is now among the most precisely known quantities in physics. Bohr's 1913 model recovered those lines by quantising angular momentum, giving a ground-state binding energy of 13.6 eV and a characteristic radius (the Bohr radius) of about 5.29 × 10−11 m. Schrödinger's 1926 wave mechanics replaced the orbits with stationary states and reproduced the same energies; the Dirac Equation of 1928 added spin and fine structure.

Two further effects made hydrogen the proving ground for quantum electrodynamics. The Lamb shift, measured by Lamb and Retherford in 1947, is a small splitting of levels that Dirac theory predicts to be degenerate, and it is attributed to interaction with the quantised electromagnetic field. The 21 cm hyperfine line at about 1420 MHz, from the flip of the electron spin relative to the proton spin, is the workhorse line of radio astronomy and maps neutral hydrogen across the galaxy and beyond.

The unresolved-looking feature that motivates most alternatives is stability. Classical Electrodynamics says an accelerating charge radiates; a classical electron in orbit should spiral into the proton in a fraction of a nanosecond. Quantum mechanics answers this by denying that the electron has a trajectory at all: the ground state is stationary and there is no lower state to radiate into. Whether that is an explanation or a restatement is exactly what is contested here.

On this wiki

The decisive question for any of these is numerical: hydrogen's level structure is known to parts in 1012, so a model that cannot reproduce the Rydberg constant, the fine structure and the Lamb shift has not yet competed with the theory it seeks to replace.

See also