Are Electrons in Stationary Atoms Always Stationary?

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In summary: It doesn't really make a difference. The binding energy of an electron is usually around 1 eV, so it's not a big deal.
  • #1
flash
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Homework Statement


When considering conservation of energy and momentum in the collision between a photon and an electron (in Compton scattering for example), is it reasonable to worry about 'stationary' electrons?

The Attempt at a Solution


From what I can recall the derivation of the Compton scattering formula was based on a stationary electron. But how is this justified? Are electrons in stationary atoms always stationary?

Thanks for any help!
 
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  • #2
by any chance do you do PHYS2013 @ ANU?

imo, It is not sensible to worry about stationary electrons. Electrons will only be stationary at absolute zero, so they’re not really worth worrying about. An electron can only be stationary if its wavelength is infinity (ie. The electron hasn’t got a definable location).
 
  • #3
flash said:
When considering conservation of energy and momentum in the collision between a photon and an electron (in Compton scattering for example), is it reasonable to worry about 'stationary' electrons?
I don't understand this question.

flash said:
From what I can recall the derivation of the Compton scattering formula was based on a stationary electron.
This is true. However, in QM, stationary is not a good concept. A related concept is the Compton wavelength, which is sometimes though of as the effective size of the particle, in the sense that, using photons as a probe, it cannot be resolved to a position more precisely than about a Compton wavelength.

flash said:
Are electrons in stationary atoms always stationary?
Well, they are bound, which is sort of like having negative kinetic energy.
 
  • #4
turin said:
I don't understand this question.
Well, they are bound, which is sort of like having negative kinetic energy.

Um, no. Bound electrons have negative energy with respect to the vacuum level, but they always have a non-negative kinetic energy.

You need to think about the energy scales involved in Compton scattering. Treating the electron as unbound is equivalent to ignoring the binding energy of the electron. Does it make much difference if we neglect the binding energy of the electron?
 

1. What is the definition of a stationary atom?

A stationary atom is an atom in which the electrons are in fixed energy levels and do not move between energy levels.

2. Are electrons in stationary atoms always stationary?

No, although the electrons in stationary atoms are in fixed energy levels, they can still move within those levels and exhibit wavelike behavior.

3. Why are electrons in stationary atoms considered to be in fixed energy levels?

This is because the electrons in stationary atoms have specific energy levels that are determined by the atom's nucleus and the laws of quantum mechanics. These energy levels are quantized, meaning they can only have specific values and cannot exist between levels.

4. Can electrons in stationary atoms change energy levels?

Yes, electrons in stationary atoms can change energy levels, but only by absorbing or emitting a specific amount of energy in the form of a photon. This process is known as electron excitation or de-excitation.

5. How do electrons in stationary atoms play a role in chemical bonding?

The arrangement and movement of electrons in stationary atoms determine the atom's chemical properties and how it interacts with other atoms. This is because the number and distribution of electrons in the outer energy levels directly impact an atom's ability to form bonds with other atoms.

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