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

A neutral hydrogen atom (H I) consists of 1 proton and 1 electron. The proton and electron spin like tops with their spin axes either parallel or anti-parallel. When hydrogen atoms switch from the parallel to the anti-parallel configuration they emit radio waves with a wavelength of 21 centimetres and a corresponding frequency of exactly 1420 MHz. This is called the 21-centimetre line. Thus, radio telescopes tuned to this frequency can be used to map the great clouds of neutral hydrogen found in interstellar space.

A photon is absorbed when an electron is raised to a higher energy level and emitted when falling to a lower level. Each element has discreet energy levels, which can be identified by looking at absorption and emission spectra so the composition of anything which emits radiation can be found.

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Paper Atomic, Ideas Internet, Word Count, sodium salt, radio telescopes, emission spectra, absorbed light, yellow light, energy level, generating laser, low temperatures, sodium vapour, photon absorbed,
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