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Calculating Ion Charge (given Electron Configuration)

  1. Jun 21, 2010 #1


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    My physics teacher told me that there was a way to calculate the ionic charge of a transition metal given its electronic configuration, but he did not tell me how, because it is 'too complicated'. I can't find any useful webpages on the subject, either... my teacher said that the subject was "too A-level" and that I don't need to know...

    I will use an example. We can figure out that iron has an electronic configuration of 1s22s22p63s23p63d8. However, it has an ionic charge of 2+ (and sometimes 3+... why can it be either?). My question is, given this piece of information, how can one calculate iron's ionic charge? Or do you need more information?

  2. jcsd
  3. Jun 21, 2010 #2


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    Well, actually (neutral) iron should be:
    1s22s22p63s23p64s23d6 (or in short [Ar]4s23d6).
    See, 4s fills up before 3d.

    I think what you're asking is 'How do you know which oxidation states are stable'?
    Well the short answer is: Experience.
    A bit more would be to say that it's very difficult because there are very many different effects involved here, mostly coming from quantum-mechanics (and in some cases, special relativity as well). If there was some kind of simple rule for it, we'd be teaching it. Of course, some rules you learn, such as noble gas configurations being are stable, mostly hold true.

    So it basically appears to be very random. Manganese will happily form a Mn(V), but Iron will practically never lose 5 electrons, even though it has one more than Manganese!
    Last edited: Jun 21, 2010
  4. Jun 27, 2010 #3


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    Thanks! Okay, so the sub-orbitals are filled in a set order? Okay, I understand. Is there a pattern? I think I remember seeing an illustration depicting the order of the different sub-orbitals.

    So it appears to be random? Okay... so what determines if, say, whether or not Fe(II) or Fe(III) will be formed? I will try to research some of these 'different effects' you describe, there must be some good e-books around.

    Also... if ionization occurs, on, say, a neutral iron atom, how do we know which electron is affected? If an electron absorbs a photon and is raised to a higher energy level, does that mean that, for example, an electron may move from 4s to 3d?

  5. Jun 27, 2010 #4


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    Staff: Mentor

    Google aufbau principle.
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