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Why does every element have it's own unique spectrum? What does happen at a sub-atomic level when absorbing and emitting light?

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    $\begingroup$ The emission spectra depends on the energy difference of the involved states of a specific element. Since different elements have different numbers of electrons and protons, the electron-electron repulsion and the electron-nucleus attraction are different for every element. $\endgroup$
    – Tobi7
    Jan 6, 2020 at 21:21
  • $\begingroup$ so the amount and configuration of electrones is corellated with the energy difference? $\endgroup$
    – Fraser
    Jan 6, 2020 at 21:23
  • $\begingroup$ Yes, a different electron configuration corresponds different energy levels, which in turn leads to a different wavelength of the emitted radiation. $\endgroup$
    – Tobi7
    Jan 6, 2020 at 21:44
  • $\begingroup$ @Tobi7, your comment reads like an adequate answer, why not post it as such and score a few points of rep? $\endgroup$ Jan 6, 2020 at 22:47

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To avoid confusion, here is a more elaborated answer. There are basically three effects that determine the energy of an atom:

  • Electron-electron-repulsion,
  • Nuclei-electron-attraction,
  • Shielding effect.

These effects depend on the number of electrons and protons and hence on the electron configuration. Just consider for example sodium and hydrogen. The energy of the hydrogen atom depends solely on the attraction of its proton and electron while in the case of sodium, the electrons repel each other and the nucleus exercises a different attraction on the inner electrons compared to the outer ones due to the shielding effect. This leads to the unique energy levels of different elements and ultimately to different emission spectra.

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  • $\begingroup$ How can an adequate answer avoid discussing the quantum mechanics of multi-electron atoms? $\endgroup$
    – ProfRob
    Jan 7, 2020 at 0:27

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