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Emission Spectroscopy or Atomic Spectroscopy

Key Concepts

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Examples of Line Emission Spectra

lithium
sodium
potassium
rubidium
cesium
calcium
strontium
barium
zinc
arsenic
selenium
wavelength 400nm450nm500nm550nm600nm650nm700nm

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Example of Element Identification

An unknown salt sample produced the line emission (atomic) spectrum shown below.

Identify the elements present.

  1. Compare the line emission spectrum of the unknown salt to the spectra of the various elements shown above.
  2. Notice that there is a red line between 600 nm and 650 nm which could correspond to the line emission spectrum of either lithium or calcium.

    lithium
    unknown
    calcium

    Most of the other wavelengths for calcium are missing from the spectrum of the unknown, so we disregard calcium and decide that lithium is one of the elements present in the sample.

  3. Next we try to match up the yellow lines, one of which appears as a band (thick line).

    Looking at the spectra of the elements above, the most likely element is potassium, so we compare the spectrum of potassium and the known.

    lithium
    unknown
    potassium

    The spectral lines of potassium are a good match for the remaining spectral lines of the unknown.

  4. The unknown salt sample contains lithium and potassium.

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Exam Questions

A written exam, test or quiz is probably printed with black ink on white paper.
For this reason, line emission (atomic) spectra will not be presented in colour.
In the exam, the spectra will be presented as either:
The process for identifying the elements present does not change.

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1. This quantisation of the amount of energy an electron can gain or lose was used as a postulate in Bohr's model of the atom.

2. This would be more correctly labelled as an absorption spectrum.