What atomic model introduced quantized electron orbits?

The Bohr model introduced quantized electron orbits, proposing that electrons could occupy only certain allowed orbits around an atomic nucleus. In 1913, Niels Bohr used this idea to explain why hydrogen emits specific spectral lines rather than a continuous range of colors.

In the model, an electron in an allowed orbit does not continuously radiate energy, despite orbiting the nucleus. Light is emitted or absorbed only when the electron jumps between allowed energy levels. The photon’s energy equals the difference between those levels, expressed as ΔE = hν. This produced the hydrogen spectrum with remarkable accuracy.

The model built on Ernest Rutherford’s 1911 nuclear atom, but it was later superseded by full quantum mechanics. Electrons are not actually tiny planets traveling along fixed circular paths; modern theory describes them with orbitals, which are probability distributions. The Bohr model remains useful as an introductory picture and gives good results for hydrogen and other one-electron, hydrogen-like ions.

The Thomson model, by contrast, placed electrons inside diffuse positive charge, while Rutherford established the compact nucleus but did not initially provide quantized orbits.