Are the electronic orbitals of an atom always quantified in the same way (i.e. the same energy required to reach the next level), or does each atom have its own values for each level?

If the quantification is universal, then the creation of photons (due to the deexcitation of the electrons) at the wavelength / color corresponding to the transition should be more abundant in the universe than all the other frequency. Except one detects no more photon of a given wavelength than of another.

So where is my reasoning error?

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    $\begingroup$ Those are the energy levels for hydrogen. $\endgroup$ – G. Smith Aug 13 at 4:36
  • $\begingroup$ If this isn't an image you made yourself, please edit your question to give proper credit to the author. $\endgroup$ – Ben Crowell Aug 13 at 15:10

The energy levels depend on two things:

  1. the electrostatic attraction between the electrons and the nucleus

  2. the electrostatic repulsion between the electrons

If you take a hydrogen atom, which is what your diagram shows, then there is a single electron and a single proton. The electron is attracted to the proton and there is no electron-electron repulsion because there is only one electron.

If you move on the the next element, helium, there are two electrons and the nucleus contains two protons. So the attraction between the electrons and the nucleus is now twice as big but we have a repulsion between the two electrons. Both these factors change the energy levels so they are not the same as hydrogen. The next element, Lithium, has three electrons and three protons in the nucleus so the energy levels are different again. And so on.

So all the atoms of a given element have the same energy levels because they have the same numbers of electrons and protons. For example all hydrogen atoms have the same energy levels. But the different elements have different energy levels because they contain different numbers of electrons and protons. The hydrogen energy levels differ from helium, which in turn differs from lithium and so on.

And just to complicate matters the number of neutrons in the nucleus makes a small difference as well, so for example the energy levels of hydrogen are slightly different from the energy levels of deuterium and tritium.

  • $\begingroup$ ok ! it's explain why there are many emission ray like : image3.slideserve.com/5438719/slide9-l.jpg right? $\endgroup$ – Matrix Aug 13 at 13:24
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    $\begingroup$ @Matrix yes. The lines in a spectrum correspond to transitions between energy levels, and since all elements have different energy levels they all have different lines in their spectra. $\endgroup$ – John Rennie Aug 13 at 13:59
  • $\begingroup$ ok, but hydrogen is the element in greater numbers in univers, so the reasoning is the same : is there no more photon in colors corresponding to the emission ray of the hydrogen in the universe? $\endgroup$ – Matrix Aug 13 at 14:20
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    $\begingroup$ Th hydrogen spectrum is actually the simplest of all the atomic spectra. That's because a lot of the energy levels in hydrogen have the same energy e.g. the $2s$ and $2p$ levels are the same energy, the $3s$, $3p$ and $3d$ levels are the same energy and so on. In atoms with more electrons the interactions between the electrons split these levels into different energies. $\endgroup$ – John Rennie Aug 13 at 14:26

The diagram you posted shows the electron energy levels for the hydrogen atom only. Other atoms will have different energy levels. Also note that the hydrogen atom itself has an infinite amount of energy levels which the diagram does not really show.

This information is very useful. The energy levels for each atom are unique, and the corresponding frequencies of light emitted by the electrons can serve as a signature of the atoms presence. This gave rise to the field of spectroscopy and it is useful in many applications. For instance, the frequencies of the light coming from other planets is used to determine the composition of the atmosphere.

  • $\begingroup$ the video where is extract this image, explain after the last level, the eectron became "free", so are you sure for your story of "infinity level"? $\endgroup$ – Matrix Aug 13 at 13:32
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    $\begingroup$ Good question. It isn't the 'last energy level' that the electron must overcome to become free, but the finite binding or ionizing energy associated to it. In the Hydrogen atom, this is 13.6eV. That means the electron needs to gain 13.6eV to become free from the Hydrogen atom. That also means there are an infinite amount of electron energy levels below 13.6eV for the Hydrogen atom $\endgroup$ – user54493 Aug 13 at 16:04

To add to @john-rennie 's answer: things get even worse as the environment of the atom makes additional modifications to the energy levels (ranging in the meV). For example, a carbon atom bound to an oxygen will have a slight energy shift compared with a free carbon atom, or a carbon atom bound in a diamond structure. These shifts are very useful in identifying molecular species.


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