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How did Niels Bohr explain stable electron energy levels?

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Bohr model diagram of a hydrogen atom showing a green nucleus labeled H, a single electron orbit, and text with atomic mass 1.008 and electron configuration 1. — atom The Bohr model describes the structure of atoms, in this case hydrogen.

In 1913, Niels Bohr addressed the instability of the Rutherford model—which predicted that orbiting electrons would lose energy and spiral into the nucleus—by proposing that electrons exist only in specific, stable "allowed" orbits.123

Bohr explained these stable energy levels through the following principles:

Quantization of Angular Momentum: Drawing on Max Planck’s work, Bohr postulated that an electron's angular momentum is quantized, meaning it can only take on discrete values. This restricts electrons to orbits of fixed sizes and energies.13
Stationary States: Electrons in these allowed orbits do not radiate energy, rendering the atom stable. The atom is most stable in the smallest orbit (the ground state), as there is no lower energy level for the electron to occupy.23
Quantum Leaps: Radiation is emitted or absorbed only when an electron abruptly jumps between these discrete energy levels. The energy of the emitted or absorbed photon corresponds exactly to the difference in energy between the two orbits.143

While this Bohr atomic model successfully explained the hydrogen spectrum, it was later superseded by more complex quantum mechanical models.143