M08 Emission spectrum: a fingerprint

Aim: To show that emission spectra of gases are unique and can be used for identification purposes

 

   If atoms and molecules are heated to sufficiently high temperatures they emit light of certain characteristic wavelengths. After resolution, the emission spectrum is observed as a number of coloured lines of specific wavelengths, on a black background. The spectrum is called an atomic emission spectrum or line spectrum. These lines are not only found in the visible range, but also in the IR and UV regions of the spectrum. The line spectrum of each element is unique. Excited sodium atoms, for example, emit light of wavelength 590nm (yellow).
Sodium discharge lamps are, for example, frequently used for lighting purposes. These are the familiar yellow lamps seen in street lamps etc.
The uniqueness of the emission spectrum allows it to be used as the basis of a method of identification of materials. In 1868 emission spectroscopy was used to identify a previously unknown element, helium (He), in the sun’s ring. Helium was later identified in the Earth’s atmosphere.