If the atom looked like a solar system, how could line spectra be explained? Line spectra are what you get when you excite gases with a high voltage. Gases emit light at only a few sharply-defined frequencies, and the frequencies are different for different gases. These emission spectra, then, are made up of a few well-defined lines.

In 1885 Johann Jakob Balmer showed that the wavelengths of light in the hydrogen spectrum could be predicted by the following equation:

Balmer series:

1 l

= R

(

1 22

-

1 n2

)

where n = 3, 4, 5, ...

R is known as the Rydberg constant, R = 1.097 x 10⁷ m^-1

The first three wavelengths in the Balmer series are:

n = 3, l = 656 nm

n = 4, l = 486 nm

n = 5, l = 434 nm

Gases will also selectively absorb light at these same frequencies. You can see this if you expose a gas to a continuous spectrum of light. The absorption spectra will be very similar to a continuous spectrum, except for a few dark lines corresponding to the frequencies absorbed by the gas.