This applet illustrates a hydrogen atom according to particle or wave model. You can choose a principal quantum number n. The right part of the graphics represents the energy levels of the atom. Right down at the bottom you can read off the orbital radius r and the total energy E.
If you try to vary the orbit's radius with pressed mouse button, this will generally lead to a non-stationary state. You can realize that by using the option "Wave model": The green wavy line which symbolizes the de Broglie wave will not be closed in most cases. Only if the circle's circumference is an integer multiple of the wavelength (blue), you will get a stationary state.
© Walter Fendt, May 30, 1999 (URL: http://www.walter-fendt.de/ph14e/bohrh.htm)
Used with permission.