What is the Correct Electron Configuration for Fe(2+)?

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Discussion Overview

The discussion centers around the correct electron configuration for the iron ion Fe(2+), exploring the principles of electron filling in atomic orbitals, particularly in transition metals. The scope includes theoretical considerations, potential exceptions to general rules, and the implications of electron interactions.

Discussion Character

  • Homework-related
  • Debate/contested
  • Technical explanation

Main Points Raised

  • One participant suggests the electron configuration for Fe(2+) as 1s2 2s2 2p6 3s2 3p6 3d3 4s2, while another source claims it is 1s2 2s2 2p6 3s2 3p6 3d6, raising questions about the order of filling orbitals.
  • Some participants propose that the filling order may not be strictly followed due to electron-electron repulsion, suggesting that energy levels are not fixed.
  • Another participant mentions that, as a rule of thumb, 4s electrons are typically lost first when transition metals form ions, although the reasoning behind this is not fully understood.
  • One participant notes that the exact electron configuration may depend on external factors such as compound symmetry and field strength, indicating that the problem may be more complex than it appears.
  • A suggestion is made to use quantum chemistry calculations, like restricted Hartree-Fock, to predict the correct configuration based on energy considerations.
  • Another participant argues that the Aufbau principle may not be reliable for heavier atoms, as interactions can lead to reversals in orbital energies.

Areas of Agreement / Disagreement

Participants express differing views on the electron configuration of Fe(2+), with no consensus reached on the correct configuration or the principles governing electron filling in transition metals.

Contextual Notes

Limitations include the potential variability in electron configurations based on external factors and the reliability of the Aufbau principle for heavier elements. The discussion reflects the complexity of electron interactions and their impact on atomic structure.

yecko
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Homework Statement


Electron configuration of Fe(2+)

Homework Equations


spdf configuration

The Attempt at a Solution


1s2 2s2 2p6 3s2 3p6 3d3 4s2

But from (https://www.thestudentroom.co.uk/showthread.php?t=1232420),
it says 1s2 2s2 2p6 3s2 3p6 3d6.
isn't electrons fill up 4s shell first, before filling up 3d shell, for more stable arrangement?
or have Cr structure of "4s1 3d5"?
thanks
 
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This is a can of worms. My bet is that the exact configuration can depend on external factors - that is, whether electrons are technically on s or d may depend on the compound, its symmetry and field strength. I would go with Ygg's rule of thumb, in general ground configuration and - in many cases - exact configuration of ions is a purely academic problem.
 
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yecko said:
But from (https://www.thestudentroom.co.uk/showthread.php?t=1232420),
it says 1s2 2s2 2p6 3s2 3p6 3d6.
If you have access to quantum chemistry package I would suggest that you try restricted Hartree-Fock calculation. Usually it predicts the correct configuration (i.e. it yields the lowest single configuration energy) as that used as general rule of thumb.
 
This is such a good question, and the answer is not very simple. I am thinking that this is somewhat technical enough to not be in a homework section.

Aufbau principle is not very reliable (Edit: they only work for very light atoms). Combination of electron-nuclear interaction and electron-electron interaction, sometimes cause reverse in the orbital energies.
 
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