[Image:Bohr-atom-PAR.svg|thumb|right|310px|The
Rutherford–Bohr model of the
hydrogen atom or a hydrogen-like ion , where the negatively charged
electron confined to an
atomic shell encircles a small, positively charged
atomic nucleus and where an electron jump between orbits is accompanied by an emitted or absorbed amount of
electromagnetic energy (
hν). The orbits in which the electron may travel are shown as grey circles; their radius increases as
n2, where
n is the
principal quantum number. The transition depicted here produces the first line of the
Balmer series, and for hydrogen it results in a photon of
wavelength 656
nm (red light).]]