Atomic spectroscopy is a chemical analysis technique and it is used to identify what elements are in a compound. It uses the idea of a photon being absorbed or emitted whenever an electron changes from one energy level to another.
The diagram below shows sodium salt being sprinkled onto a flame and yellow light being emitted.
Emission spectra are produced by thin gases in which the atoms do not experience many collisions (because of the low density). The emission of yellow light occurs because the electrons of the sodium salt have been promoted to a higher electronic energy state but have then fallen back down and emitted the energy as an electromagnetic wave, in the wavelength corresponding to yellow which is » 600 nm. The more intense that the yellow band is the more abundant the sodium salt present.
The diagram (left) shows an atomic excitation
caused by the absorption of a photon and an atomic
de-excitation caused by emission of a photon.
In each case the wavelength of the emitted or absorbed
light is exactly such that the photon carries the energy
difference between the two orbits. This energy may be
calculated by multiplying the Plank constant by the
wavelength of the light. Thus, an atom can absorb
or emit only certain discrete wavelengths
(or equivalently, frequencies or energies).
This diagram shows white light being shone through sodium vapour and the resulting spectra on a board.
An absorption spectrum occurs when light passes through a cold, dilute gas and atoms in the gas absorb at characteristic frequencies; since the re-emitted light is unlikely to be emitted in the same direction as the absorbed photon, this gives rise to dark lines (absence of light) in the spectrum.
Absorption spectroscopy can only be carried on a substance in solution or gaseous form.
The presence of the dark band shows that the sodium vapour had absorbed t
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