I am a chemistry student, and my current are of study is mass spectrometry.

In the ionization process, atoms are bombarded with electrons, but how does this work? I assume the flow of electrons attract the electrons of the atom, thereby removing them, but where do the atom's electrons go?

  • $\begingroup$ Electrons do not attract electrons, they would repel each other as they have like charge. $\endgroup$ – Sherlock Holmes Oct 15 '14 at 1:28
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    $\begingroup$ Imagine the analogy of you holding on to an object (let's say your groceries) then someone chucks stuff at you. You might accidentally drop the groceries. While this is obviously not an accurate analogy on an atomic level, it might help to visualise what is going on. $\endgroup$ – robertmartin8 Oct 15 '14 at 11:01

This type of ionization is known as electron ionization (there are many types of ionization methods used for MS). One possible reaction for EI is: $$\ce{M +e- ->M^{•+} +2e-}$$ source

If the incoming electron has the correct energy to interact and passes close enough to the molecule, it's electric field can impart enough energy to one of the molecule's electrons for it to be ejected. What happens to the electrons after that isn't particularly important as far as ionization is concerned, but in most EI sources, electrons are emitted perpendicular to the axis of the sample source and are collected on the other side by an electrode, preventing charging of the source chamber and focusing the emitted electrons into a beam.

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  • $\begingroup$ A lot of people call it "electron impact ionization" or "EI" instead of just "electron ionization". $\endgroup$ – Curt F. May 18 '15 at 4:18
  • $\begingroup$ Yes, that's the older term for it. IUPAC discourages its use now. $\endgroup$ – Michael DM Dryden May 18 '15 at 21:58
  • $\begingroup$ Interesting. I don't understand the reason for half the stuff IUPAC does. Why would they do that? $\endgroup$ – Curt F. May 19 '15 at 3:55
  • $\begingroup$ "Note: Electrons and photons do not "impact" molecules or atoms. They interact with them in ways that result in various electronic excitations including ionization. For this reason it is recommended that the terms 'electron impact' and 'photon impact' not be used."—from Recommendations for nomenclature and symbolism for mass spectroscopy $\endgroup$ – Michael DM Dryden May 19 '15 at 17:42
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    $\begingroup$ It's my experience that chemists ignore or simply aren't aware of a lot of IUPAC recommendations and I don't think it's a big deal in this case. But the difference, of course, in the two examples is that a classical collision model is a very good explanation for a macroscopic baseball but fails to correctly describe much of the behaviour of a photon or electron interacting with an atom. $\endgroup$ – Michael DM Dryden May 19 '15 at 18:29

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