question about energy levels and line spectra

[gib65]

There are different spectral lines for each element, right? These spectral lines are explained by the Bohr model of the atom, right? That is, the Bohr model says that electrons drop from one energy level to another, and these drops are accompanied by the emission of photons carrying an amount of energy equal to the difference between the two energy levels. Because there are only a few such energy levels, the electrons can only emit photons of certain energy amounts (i.e. only certain wavelengths/frequencies). These wavelengths/frequencies are what cause the spectral lines.

 

Here's my question: since each element creates different spectral lines, the energy difference between each level can't be the same for all elements, can it? For example, suppose you burnt hydrogen gas, and one spectral line is created by a photon emitted from an electron that dropped from energy level n=2 to energy level n=1. Now suppose you burnt helium gas, and one spectrial line, which has to be a different one from those of hydrogen, is created by a photon emitted from an electron that dropped from the same energy levels n=2 to n=1. It's the same energy levels but a different spectral line. This means the photons emitted in each case must carry different energy amounts, and this means the difference in energy between energy levels must not be the same from one element to another. Is this true?

[swansont]

The Bohr model (which is only an approximation anyway) varies with Z and only has validity for single-electron systems. The interaction of the other electrons affects the sprectra, as do interactions not included in the Bohr model.

[gib65]

The interaction of the other electrons affects the sprectra

 

So could we say, then, that the particular lines that we see in the spectra depend on the atomic number?

 

Also, what is 'Z'?

[insane_alien]

z is the number of protons.

[MrSandman]

The interaction of the other electrons affects the sprectra,

 

 

Thus giving you different light spectrums. However, does isotopes also give different light spectra? Accordding to what you said it would.

[insane_alien]

no it doesn't and nothing swansont said indicated that the number of neutrons has anything to do with it.

[MrSandman]

Ok, what about ions and anions?

 

Well about the isoptopes. The number of neutrons would cause the electrons to interact differently wouldn't it? Because the amount of energy between the neutrons and electrons would vary. But would this not be enough to change the spectrum?

[insane_alien]

yeah, ions will have different spectra because your changing the number of electrons present.

 

neutrons only interact with electrons through gravity. we have nothing sensitive enough to pick up any effect it could possibly have by several orders of magnitude. for all intents and purposes neutrons have no effect.

[MrSandman]

Or does that mean it has very, very, very little effect? Considering also that light is effected by gravity, but it still not enough to see a difference.

[swansont]

Thus giving you different light spectrums. However, does isotopes also give different light spectra? Accordding to what you said it would.

 

i_a is right in that I did not mention anything about isotopes, but there is an effect, though it's small. The nucleus is a finite object (not a point) so changing the numbers of neutrons will vary the charge distribution, and this will have a subtle effect on the energy levels. So there is an "isotope shift" in the line spectra.

 

As I recall it's small; when I was trapping radioactive K-37 and K-38 the shift had to be predicted so we'd know where to look; it hadn't been measured prior to that. I think it was a few tens or hundreds of MHz for an optical transition (at somewhere around 770nm, IIRC. Don't have the paper handy) so something like a ppm shift.

[MrSandman]

So I did get my points straight, thanx. I just did a lab with light spectrums in different plants. Through my discoveries they was evidently an oil smudge on the test tube. Making a hole(dip) in my graph. But however the chemical composition of all of them were similiar thus supporting elements have the same light spectrum.