Balmer formula
A simple whole-number formula giving the wavelengths of the visible lines in hydrogen's light, found in 1885 by the Swiss schoolteacher Johann Balmer.
In 1885 Johann Balmer, a schoolteacher in Basel, reported that the wavelengths of hydrogen's four lines match a reference length multiplied by m×m divided by (m×m − 4), for m = 3, 4, 5 and 6[1]. The longest of them is the red line at 656 nanometres.
The formula worked, but there was no reason behind it. In 1913 Niels Bohr proposed that light is emitted when an electron jumps between states of fixed energy, and derived the formula from the electron's mass and charge and Planck's constant[2].
Related families of lines exist too: the Lyman series in the ultraviolet, the Paschen series in the infrared, and others. Each corresponds to a different state that the electron jumps down to.
Related terms
- Bohr modelThe 1913 model in which electrons circle only on certain orbits and emit light of definite energy when jumping between them.
- SpectrumLight spread out by wavelength (colour). Atoms and molecules each emit and absorb only certain wavelengths, so thin lines appear in the spectrum.
- Planck constantThe fundamental constant, written h, that sets the step size of energy for light and matter. Frequency times h is the smallest unit of energy for that light.