Can I only use planck's equation (E = hf) to measure the energy of a photon or can it also be used to measure the energy of an electron in an atom? F.e. if given the linespectrum of a light coming from a Na atom, what would be the meaning of the E calculated for each frequency?

Question

anonymous · Answer

In other words: is there any important link between "the smallest energy packet for a certain frequency" and the energy an exited electron releases when it falls back to it's initial energy level?

jfraser · Answer

that's exactly how the relationship was created. The energy of a photon emitted from an atom is $exactly$ equal to the energy lost  by the electron when it transitioned from a high energy state to the lower energy state

kainui · Answer

@heledommejongen Some points I want to clarify for you:

If you refer back to he equation E=hf this means a certain frequency IS a certain energy. What you have said, "the smallest energy packet for a certain frequency", implies that it might be possible for E>hf as well, which is not true. All light of the same frequency has the same amount of energy.

"...an exited electron releases when it falls back to it's initial energy level" When electrons are excited, they don't necessarily fall back down to their initial energy level. For example, they might be excited up 2 energy levels and only fall down by 1 energy level, which is exactly how you end up with different frequencies in the spectrum, since smaller energy difference will give rise to a smaller frequency of light emitted! =D