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Confused about magnesium's and calcium's emission spectra

  1. Oct 15, 2016 #1
    I have read that magnesium’s flame is white, and the light emitted includes all the wavelengths of visible light. Calcium, on the other hand, needs less energy to excite its valence electron, and hence, during emission, the radiation given off has a longer wavelength (red light) and its flame is red/orange.

    However, I got confused when I looked up the emission spectra for both:
    http://alexpetty.com/content/images/2014/09/Figure-20--The-light-signature-of-Calcium.png
    http://alexpetty.com/content/images/2014/09/Figure-12--The-light-signature-of-Magnesium.png

    Magnesium's spectrum shows less wavelengths than calcium's, which appears to emit also blue and green light (which have higher energy) at many more wavelengths. Based on these spectra, I would expect calcium to be the one to burn with a white flame...? Why is it still red/orange? And magnesium certainly does not appear to emit radiation at "all wavelengths of visible light"; I guess my book's wording is misleading?

    Also, am I correct to say that elements show these different wavelengths because not only is the valence electron(s) excited when the substance is burned, for example, but also lower energy electrons => hence, we have different energy differences => radiation of different wavelengths is emitted?

    All help is very much appreciated!
     
    Last edited: Oct 15, 2016
  2. jcsd
  3. Oct 15, 2016 #2

    Borek

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    Staff: Mentor

    You are mistaking emission spectra of the elements with the thermal emission of the burning metal (or any substance burning as hot as magnesium).
     
  4. Oct 15, 2016 #3
    Aren't they related? Still a bit lost... Thank you for the response anyway!
     
  5. Oct 15, 2016 #4

    Borek

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    Staff: Mentor

    In general - no.

    Sure, as the heated element emits a bit on its own, its emission spectrum is present in the spectrum of the burning substance. But the thermal emission is - especially in the cases involved - much, much stronger.
     
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