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Electron shell, Oxidation number

  1. Jan 6, 2016 #1
    Dear PF Forum,
    I think I have asked too many question for one day.
    I'm trying to understand antioxidant and free radicals. But, first I'd like to understand oxidation number.
    The oxidation number for hydrogen is +1 or -1. I can understand that. Either Hydrogen must lost one electron or gains one electron to complete its shell.
    Helium is, of course, zero
    Lithium, 1s2 2s1, is +1. I can understand that from its electron configuration.
    Beryllium, 1s2 2s2, +2, also obvious.
    Oxygen, -2, but sometimes -1 or +2
    Fluor, -1.
    Now, about Nickel:
    http://www.thecatalyst.org/oxnotabl.html states that Nickel oxidation number is +2

    1s2 2s2 2p6 3s2 3p6 3d8 4ss is +2

    My question is:
    1. Why that website doesn't also state that Nickel oxidation number is +1 also, because
    states that one of Nickel electron configurations is as follows.
    1s2 2s2 2p6 3s2 3p6 3d9 4s1

    2. Why nickel electron configuration is
    1s2 2s2 2p6 3s2 3p6 3d8 4ss
    Why not
    1s2 2s2 2p6 3s2 3p6 3d10

    Why Nickel doesn't complete its 3d shell with 10 electron?
    Or the 'why' word here is the wrong question. Because the answer is: it is so!

    Thanks for any help.
  2. jcsd
  3. Jan 6, 2016 #2


    User Avatar

    Staff: Mentor

    Or 0. Every element when not in compounds has by definition oxidation number of zero.

    Don't pay too much attention to oxidation numbers - they don't exist in reality. There is no measurable physical quantity that can be attributed to them. They are useful as an accounting device when it comes to balancing redox equations, but even then we can use other methods.

    Because the 4s has a slightly lower energy and is filled first. Look for Aufbau principle.
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