- a theory of atomic structure in which the hydrogen atom (Bohr atom) is assumed to consist of a proton as nucleus, with a single electron moving in distinct circular orbits around it, each orbit corresponding to a specific quantized energy state: the theory was extended to other atoms.
- a theory of atomic structure that explains the spectrum of hydrogen atoms. It assumes that the electron orbiting around the nucleus can exist only in certain energy states, a jump from one state to another being accompanied by the emission or absorption of a quantum of radiation
- An early model of atomic structure, in which electrons circulate around the nucleus in discrete, stable orbits with different energy levels. This model was the first to predict and explain the atomic spectrum of the hydrogen atom, which arises as the electron jumps from one orbit to another orbit of lower energy, giving off electromagnetic radiation of predictable frequencies. Later models of atomic structure abandoned the idea of circular orbits, and explained the stable orbits as standing waves. See also atomic spectrum orbital.