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When an electron absorbs a photon, does the photon become electron "stuff" (energy); or, is it contained within the electron as a discrete "something"?

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the nature of the electron does not change but it move s higher energy orbit within the atom –  user13267 Mar 31 at 6:18
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When an electron absorbs a photon, it remains an electron and the photon disappears. The electron energy and momentum are altered to account for the energy and momentum the photon was carrying. For a free electron, it will not be possible to balance energy and momentum simultaneously. There will have to be another interaction to make that work. If the electron is part of an atom, it can transfer some of the momentum to the rest of the atom and it can balance.

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One should note that exists no conservation law for the number of photons the way there exists one for the number of electrons (no "photon number conservation" as "lepton number conservation" ) –  anna v Mar 31 at 4:19
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Perhaps worth adding that the electrons angular momentum must also change to account for that of the photon. This can be either a spin flip or a change of orbital angular momentum in some system. –  dmckee Apr 1 at 1:58
    
@Ross Millikan, I think Asker wants to know when two elementary particles assemble why do we get still an elementary particle instead of a composite particle.So the answer should be more on "why" part. –  user22180 Apr 4 at 19:38
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As Ross pointed out, two scenarios are possible: free electron / electron as part of an atom. They're treated in two totally different ways.

  • Free electron: free electrons can't really "absorb" photons. They can collide with them, and some things can happen (this, for instance). Those types of collisions are described by QED and there are a bunch of conservation laws which govern them – lepton number, spin, energy, momentum, etc..
  • Electron as part of an atom: this is probably the case you want. In its description the photon is not treated as a "particle" (in the QED sense, but even the classical "colliding spheres" analogy doesn't hold), and you sort of see it as a unit of energy (the "discrete something", a wave, pretty much) which gets delivered to the electron, which goes to a higher (read: less stable) energy level and then decides what to do: it can go back to where it was (spitting out another photon, i.e. energy), drift away (should the photon beat the electron's ionisation energy, this is the case for X and gamma radiation) or, ultimately, stay, until something else happens.
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You can also have electrons in an electric or magnetic field. –  Aron Mar 31 at 12:10
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Yes; there are also many other circumstances (semiclassical models etc.), but judging on the "basic" level of the question it's probably best to disregard them for now..! –  marco Mar 31 at 12:23
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Note that electron in isolation can never absorb or emit a photon.

It is only a system of 2 particles (*) than can.

P.S. 2 or more; Theoretical consideration of electron in a static field requires something to create said field.

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protected by Qmechanic Mar 31 at 18:21

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