Line emission spectra

When an atom or ion is heated in a Bunsen or an electric current is passed through it the electrons within it become excited. This means that they jump out form their normal ground states close to the nucleus to excited states further from the nucleus. This takes energy which is provided by the heat or electricity. Shortly afterwards the excited electrons will fall back to their ground states and release the gained energy as a photon of light. If these photons are in the visible region of the spectrum a colour is seen. The animation is a representation of this process.

Animation - origin of line emission spectra

When the line emission spectrum is viewed through a spectroscope the individual lines of colour can be seen. You can find some pictures of line emission spectra on the centre pages of the Nuffield Data Book. The presence of individual lines of colour, as opposed to a continuous band of colour, is very important as it indicates something fundamental about the structure of the atom. It tells us that the electrons in atoms have fixed energy levels.