Johann Jacob Balmer

Atomic Spectra (Johann Jacob Balmer)

After chemists and physicists began using the spectroscope to catalog the wavelengths of the light either emitted or absorbed by a variety of compounds, these data were then used to detect the presence of certain elements in everything from mineral water to sunlight. No obvious patterns were discovered in these data, however, until 1885 when Johann Jacob Balmer analyzed the spectrum of hydrogen.

When an electric current is passed through a glass tube that contains hydrogen gas at low pressure the tube gives off blue light. When this light is passed through a prism as shown below, four narrow bands of bright light are observed against a black background. These narrow bands have the characteristic wavelengths and colors shown in the table below. Balmer noticed that these data fit the following equation to within 0.02%.

eqn6_12.gif (944 bytes)

 

In this equation, RH is a constant known as the Rydberg constant, which is equal to 1.09678 x 10-2 nm-1, and n is an integer between 3 and 6.

The Characteristic Lines in the Visible Spectrum of Hydrogen

Wavelength (nm) Color
656.2 red
486.1 blue
434.0 blue-violet
410.1 violet

 

fig6_11.gif (35077 bytes)

The blue light given off when a tube filled with H2 gas is excited with an electric discharge can be separated into four narrow bands of light when it is passed through a prism.

 

books.gif (1982 bytes)

History of Chemistry

magnifyingglass.gif (354 bytes)

Experiments Index

einstein.gif (32471 bytes)

Scientists Index