Why does the emission spectra of an element contain more than one line?

Question

My question is simple, yet a thorough search of Google brought me no closer to finding the answer. I found countless articles explaining what the emission spectra of an element was, but none which satisfactorily told me why they contained more than one line.

I understand the core concept. That is, if you add energy to an atom, which may be the heat from the Bunsen flame, the atoms will gain that energy and their electrons may be promoted to a higher energy level. Since this energy level is unstable the excited electrons return to their stable state, emitting energy as visible light, the frequency of which directly relates to difference between energy levels.

My question is do all the electrons jump when energy is applied to them? Do only a selected few jump? Are the jumps for a particular element consistent? What precisely produces the unique spectra for each element? Why, my brain moans to find the answer!

Smart answers please, I also thank you in advance.

Doctor Q, you have almost answered my question but you're not quite there yet. For example, let's take the emission spectra of hydrogen. The emission spectra contains 4 distinct lines as shown on the Wikipedia entry http://en.wikipedia.org/wiki/Emission_spectrum, which represent four discrete wavelengths of light. Since hydrogen only has one electron in its orbit wouldn't it make sense that the emission spectra of hydrogen would only have one line? After all, the hydrogen atom will absorb a specific amount of energy it's electron will make a specific jump? I am a high school student in year 12, so you may need to a little easy explaining, which you've done a very good job of so far. Also, we've only stated learning about this topic in chemistry and my teacher was not able to explain it to me satisfactorily. Thanks in advance.

Answer 1

I think you have answered your own question.

You are right that electrons transferring to and from different energy levels either absorb or release photons of certain energies and frequencies.

When you have an amount of a substance, you have literally billions of atoms (not just one), each having electrons going through different transitions at different times. That is why certain materials have differing line spectra due to the 'allowed energy levels' within that specific atom.

Hydrogen has completely different allowed energy levels to helium and so on.

The allowed energy levels are governed by the allowed Quantum numbers for the particular atoms, regarding the magnetic moment and spin of particular electron orbits. The electrons must have discreet energy levels i.e. they can only be of a certain value - the energy range is not continuous.

Say for hydrogen-:
n=1 -13.6eV
n=2 - 3.4 eV
n=3 - 1.5 eV

A transition from n=3 to n=2 releases a specific amount of energy, in this case -1.8 eV, which then corresponds to a certain photon frequency which will be released. A transition from n=3 to n=1 (- 12.1 eV) would be a completely different photon emission, thus the different line spectra are produced.

Remember only the Balmer Series of transitions emits photons in the visible range, most other series emit in the Infra-Red (Paschen Series) or Ultra Violet (Lyman Series) range.

Hope this helps.

Answer 2

An element emits light when an electron decays (gone from a high energy level to a low energy level). So an electron in an atom going from energy level 5 to 3 (or whatever) gives off a specific wavelength of light for that specific element. It would give off a different wavelength of light for a different element because the mass of the nucleus would change. If the nucleus has more mass than more energy is given off when the electron decays. That is that there is a larger difference in energy between energy levels in a large atom than a small one. Basically because the electrons in different elements are being pulled towards the nucleus with different strengths, they have different energies which translates into different wavelengths of light.