Confused about magnesium's and calcium's emission spectra

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Discussion Overview

The discussion centers on the emission spectra of magnesium and calcium, particularly in relation to their flame colors and the underlying reasons for these observations. Participants explore the differences in energy requirements for electron excitation and the implications for the emitted light's wavelengths.

Discussion Character

  • Exploratory
  • Technical explanation
  • Conceptual clarification
  • Debate/contested

Main Points Raised

  • One participant notes that magnesium's flame appears white and emits all visible wavelengths, while calcium's flame is red/orange due to lower energy requirements for exciting its valence electron.
  • The same participant expresses confusion regarding the emission spectra, observing that magnesium's spectrum shows fewer wavelengths than calcium's, which includes blue and green light.
  • The participant questions the accuracy of their textbook's claim that magnesium emits radiation at "all wavelengths of visible light."
  • Another participant suggests that the emission spectra of the elements should not be confused with the thermal emission from burning substances, indicating a distinction between the two phenomena.
  • A later reply emphasizes that while the heated element's emission spectrum is present, thermal emission is significantly stronger in these cases.

Areas of Agreement / Disagreement

Participants do not reach a consensus, as there are differing views on the relationship between emission spectra and thermal emission, with some confusion remaining about the implications of the observed spectra.

Contextual Notes

There are unresolved questions regarding the definitions of thermal emission versus emission spectra, and the discussion highlights the complexity of how different energy levels of electrons contribute to the observed emissions.

nucleon
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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-12--The-light-signature-of-Magnesium.png%29,
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
http://alexpetty.com/content/images/2014/09/Figure-12--The-light-signature-of-Magnesium.png%29,
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!
 
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You are mistaking emission spectra of the elements with the thermal emission of the burning metal (or any substance burning as hot as magnesium).
 
Aren't they related? Still a bit lost... Thank you for the response anyway!
 
nucleon said:
Aren't they related?

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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