Editing Bohr model (section)

{{Short description|Atomic model introduced by Niels Bohr in 1913}}
{{Redirect|Bohr's law}}
{{Distinguish|Bohr equation|Bohr effect}}
[[Image:Bohr atom model.svg|thumb|310px|The Bohr 
model of the [[hydrogen atom]] ({{nowrap|''Z'' {{=}} 1}}) or a hydrogen-like ion ({{nowrap|''Z'' > 1}}), where the negatively charged [[electron]] confined to an [[atomic shell]] encircles a small, positively charged [[atomic nucleus]] and where an electron jumps between orbits, is accompanied by an emitted or absorbed amount of [[electromagnetic wave|electromagnetic energy]] (''h&nu;'').<ref name="Akhlesh Lakhtakia Ed. 1996">{{Cite journal |last1=Lakhtakia |first1=Akhlesh |last2=Salpeter |first2=Edwin E. |year=1996 |title=Models and Modelers of Hydrogen |journal=American Journal of Physics |volume=65 |issue=9 |pages=933 |bibcode=1997AmJPh..65..933L |doi=10.1119/1.18691}}</ref> The orbits in which the electron may travel are shown as grey circles; their radius increases as ''n''<sup>2</sup>, where ''n'' is the [[principal quantum number]]. The {{nowrap|3 → 2}} transition depicted here produces the first line of the [[Balmer series]], and for hydrogen ({{nowrap|''Z'' {{=}} 1}}) it results in a photon of [[wavelength]] 656&nbsp;[[nanometre|nm]] (red light).]]

In [[atomic physics]], the '''Bohr model''' or '''Rutherford–Bohr model''' was the first successful model of the [[atom]].  Developed from 1911 to 1918 by [[Niels Bohr]] and building on [[Ernest Rutherford]]'s nuclear [[Rutherford model|model]], it supplanted the [[plum pudding model]] of [[J.&nbsp;J. Thomson]] only to be replaced by the quantum atomic model in the 1920s. It consists of a small, dense nucleus surrounded by [[orbit]]ing electrons. It is [[analogy|analogous]] to the structure of the [[Solar System]], but with attraction provided by [[Coulomb's law|electrostatic force]] rather than [[gravity]], and with the electron energies quantized (assuming only discrete values).

In the history of atomic physics, it followed, and ultimately replaced, several earlier models, including [[Joseph Larmor]]'s Solar System model (1897), [[Jean Perrin]]'s model (1901),<ref>{{Cite journal |last=Perrin |first=Jean |author-link=Jean Baptiste Perrin |year=1901 |title=Les Hypothèses moléculaires |url=https://fr.wikisource.org/wiki/Les_Hypoth%C3%A8ses_mol%C3%A9culaires |journal=La Revue scientifique |page=463}}</ref> the [[Cubical atom|cubical model]] (1902), [[Hantaro Nagaoka]]'s [[Saturn]]ian model (1904), the plum pudding model (1904), [[Arthur Haas]]'s quantum model (1910), the [[Rutherford model]] (1911), and [[John William Nicholson]]'s nuclear quantum model (1912). The improvement over the 1911 Rutherford model mainly concerned the new [[quantum mechanics|quantum mechanical]] interpretation introduced by Haas and Nicholson, but forsaking any attempt to explain radiation according to [[classical physics]].

The model's key success lies in explaining the [[Rydberg formula]] for [[Hydrogen spectral series|hydrogen's spectral emission lines]]. While the Rydberg formula had been known experimentally, it did not gain a theoretical basis until the Bohr model was introduced. Not only did the Bohr model explain the reasons for the structure of the Rydberg formula, it also provided a justification for the fundamental physical constants that make up the formula's empirical results.

The Bohr model is a relatively primitive model of the hydrogen atom, compared to the [[Valence electron#Valence shell|valence shell]] model. As a theory, it can be derived as a [[Orders of approximation#First-order|first-order approximation]] of the hydrogen atom using the broader and much more accurate quantum mechanics and thus may be considered to be an [[obsolete scientific theory]]. However, because of its simplicity, and its correct results for selected systems (see below for application), the Bohr model is still commonly taught to introduce students to quantum mechanics or [[Energy level#Energy level diagrams|energy level diagrams]] before moving on to the more accurate, but more complex, valence shell atom. A related quantum model was proposed by [[Arthur Erich Haas]] in 1910 but was rejected until the 1911 Solvay Congress where it was thoroughly discussed.{{sfn|de Broglie|Langevin|Solvay|Einstein|1912|pp=122–123}} The quantum theory of the period between [[Max Planck#Black-body radiation|Planck's discovery of the quantum]] (1900) and the advent of a mature quantum mechanics (1925) is often referred to as the ''[[old quantum theory]]''.