Old quantum theory

<p>The old quantum theory is a collection of results from the years 1900–1925, which predate modern <a href="/facts/Quantum_mechanics/BRc3Mzgr">quantum mechanics</a>. The theory was never complete or self-consistent, but was instead a set of <a href="/facts/Heuristic/BcBEkv9c">heuristic</a> corrections to <a href="/facts/Classical_mechanics/ykG8upsN">classical mechanics</a>. The theory has come to be understood as the <a href="/facts/WKB_approximation/XyRnYvGh">semi-classical approximation</a> to modern quantum mechanics. The main and final accomplishments of the old quantum theory were the determination of the modern form of the periodic table by <a href="/facts/Edmund_Stoner/30kenmeg">Edmund Stoner</a> and the <a href="/facts/Pauli_exclusion_principle/lsBKGeHD">Pauli exclusion principle</a>, both of which were premised on <a href="/facts/Arnold_Sommerfeld/cJtpVHvn">Arnold Sommerfeld</a>'s enhancements to the <a href="/facts/Bohr_model/FmTHjaxy">Bohr model</a> of the atom.
</p><p>The main tool of the old quantum theory was the Bohr–Sommerfeld quantization condition, a procedure for selection of certain allowed states of a classical system: the system can then only exist in one of the allowed states and not in any other state.
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Old quantum theory open-in-new

Old quantum theory