Electron Affinity, Type of energy released?

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Discussion Overview

The discussion centers around the concept of electron affinity, specifically the nature of the energy released when an atom, such as oxygen, gains an electron to form an anion. Participants explore the forms of energy involved in this process, including heat, light, and kinetic energy, as well as the implications of electron transitions and radiation.

Discussion Character

  • Exploratory
  • Technical explanation
  • Conceptual clarification

Main Points Raised

  • One participant questions the form of energy released during the formation of an anion from an atom gaining an electron, wondering if it involves emitted photons or changes in mass.
  • Another participant suggests that the energy is released as heat and light, indicating that the process is exothermic and that the specifics depend on the reaction.
  • A participant describes the energy transformation as involving the exchange of electromagnetic potential energy (EM-PE) for kinetic energy (KE) as the electron and atom approach each other.
  • It is noted that while the electron accelerates, it radiates energy, resulting in the emission of infrared photons and an anion with additional random kinetic energy.
  • A participant inquires about the existence of a formula similar to the Rydberg formula for hydrogen that applies to oxygen, indicating interest in energy levels associated with electron transitions.
  • Another participant confirms that there are energy levels for oxygen and describes the process of the electron transitioning from a higher orbital to a lower one, emitting photons during these transitions.
  • It is mentioned that the kinetic energy transferred to the oxygen atom is typically very small due to the mass difference between the oxygen atom and the electron.
  • A participant introduces the idea of shooting low-energy electrons at oxygen, suggesting that this could lead to electrons in excited states of the anion due to recoil effects.

Areas of Agreement / Disagreement

Participants generally agree on the exothermic nature of the process and the involvement of energy transformations, but there are varying perspectives on the specifics of the energy released and the mechanisms involved. The discussion remains unresolved regarding the exact nature of the energy forms and their implications.

Contextual Notes

There are limitations in the discussion regarding the assumptions made about energy transformations, the dependence on specific reactions, and the lack of detailed mathematical descriptions of the processes involved.

mishima
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This might be a dumb question, but for instance when oxygen gains an electron to become an anion, energy is released equal to its electron affinity. What exactly is the form of this energy? Is there a photon of a certain wavelength emitted? Does the anion slow/cool down because of the small increase in mass? Thanks for any insight.
 
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It's a good question - you should be interested in the energy transformations.

Ultimately the energy is released as heat (and light) - hence the process is exothermal.
The details of the process depends on the specific reaction.
In chemistry you are not normally worried about these details.

Related concept: "free energy of binding".

Simplistically: you could imagine it as the O and e- are initially at rest close to each other.
Since conditions favor forming an anion, they initially accelerate towards each other - exchanging EM-PE for KE until the balance of PE and KE matches an available stationary state.

While the e- is accelerating, it radiates.
The end result is some, usually IR, photons from the radiation and an anion with some additional, random, KE.
 
Simon Bridge said:
While the e- is accelerating, it radiates.
The end result is some, usually IR, photons from the radiation and an anion with some additional, random, KE.

That makes sense. I wasn't sure if there was something like the Rydberg formula for hydrogen that applies to oxygen.
 
There is - with different energy levels.

You can think of it as the extra electron is initially in a far-away orbital and decays into a lower orbital.
At each step it releases a photon - depending on the transitions.

What I did before was the quasi-classical description of the same thing - electron radiates when it is not in a stationary state.

Note: The KE transferred to the oxygen is usually very very small since the mass of O is much bigger than the mass of a single e- so we would normally ignore it. I just thought it would be nice to have a tie into something less mysterious to you :)

You can also imagine shooting (low energy) electrons at oxygen - in which case you'll get many electrons in excited states of the anion due to recoil effects from the electrons initial KE.
Indeed do many things come to pass.
 

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