# Formula Rydberg Formula for Hydrogen Wavelength    Principal quantum number    Upper principal quantum number    Rydberg constant ## Wavelength

Unit
Wavelength of electromagnetic radiation in vacuum with which the H atom is irradiated. The wavelength is related to the energy of the radiation as follows: $$W ~=~ h \, \frac{c}{\lambda}$$. Thus, from the radiation of wavelength $$\lambda$$ absorbed by the H atom, the energy absorbed by the H atom can be calculated.

## Principal quantum number

Unit
This is an integer indicating an energy level of the H atom. The electron in the H atom can occupy an energy state, which is described by $$n$$.

It is true: $$n ~\lt~ m$$, that is, the $$n$$th energy state is lower than the $$m$$th energy state. The electron in the H atom can be excited to the $$m$$th energy state.

## Upper principal quantum number

Unit
Upper principal quantum number is an integer indicating an energy level of the H atom. The electron in the H atom can occupy this energy state, which is described by $$m$$, by being excited into this energy state by a photon. After a short time, the electron falls back to the lower state $$n$$ and the H atom emits a photon in the process. The energy of this photon corresponds to the difference of the energy between $$m$$ and $$n$$ states.

## Rydberg constant

Unit
Rydberg constant for the H atom is: $$R = 1.097 373 15 \,\cdot\, 10^7 \, \frac{1}{\mathrm m}$$. It is expressed in units of wavenumber and multiplied by Planck's constant $$h$$ and the speed of light $$c$$, it gives energy necessary to remove the electron from the H atom (i.e., to ionize the H atom):$$R \, h \, c ~=~ 2.17 \cdot 10^{-18} \, \mathrm{J} ~=~ 13.6 \, \mathrm{eV}$$