SPECTROSCOPY - The study of spectral lines
SPECTRAL LINES - These spectral lines are produces by "exciting" gas atoms and molecules with high voltage (about 5000 volts). This energy kicks electrons to higher energy levels where they are unstable and drop back towards the ground state (lower energy levels). As the electrons make this downward transition, they release energy in the form of visible light.
The photographs of the spectral lines were taken through diffraction grating. The diffraction grating splits the light into its component colors. Each of the spectral lines is an image of the gas discharge tube (left photo). If the tube was a circle instead of a narrow tube, the spectral "lines" would be circles. Obviously it is easier to distinguish spectral lines if they are narrow and distinct.
The colors of the spectral lines are dependent on the distance the electron drops as it cascades to the ground state. These drops are determined by the electron configuration of each atom and the spectral lines are unique to that atom. A small drop produces a low energy photon - red. While a larger drop towards the ground state produces a higher energy photon - blue.
As
you can see in these images, there are many possible transitions of the
electrons towards the ground state. Also note that each spectrum is
different. Each atom (or molecule) is different.
Nucleus
This diagram represents an atom with a positively charged nucleus and electrons in high energy orbitals (about to drop towards the ground state).
The electron gained energy to achieve the higher energy status and will release the energy when it drops to the lower level.
The energy of the electron is quantitized. It takes a discrete amount of energy to lift the electron and it releases a definite amount of energy when it drops to the ground state. Because of the unique structure of the elements, each spectrum is unique.
EMISSION SPECTRUM FOR A FEW GASES
ARGON
CARBON DIOXIDE
HYDROGEN
MERCURY
NEON
NITROGEN
OXYGEN
XENON