Bohr Model
The 1913 model in which electrons orbit the nucleus in fixed circular paths of quantised energy and angular momentum.
Formula / equation
mvr = nh / 2π
Unit
Dimensionless
In depth
Bohr postulated that electrons radiate energy only when jumping between allowed orbits, which explained the hydrogen emission spectrum with remarkable precision. The model fails for atoms with more than one electron and cannot account for spectral fine structure, but it introduced quantisation into atomic theory for the first time.
Examples in the real world
An electron falling from n = 3 to n = 2 in hydrogen emits the red 656 nm line of the Balmer series.