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Homework Help: Question on Electron Configuration

  1. May 30, 2012 #1
    1. The problem statement, all variables and given/known data
    What is the electron configuration for Ti+2? The answer to this question, from my homework, is [Ar]3d2, but I am not able to figure out why.

    2. The attempt at a solution
    I originally thought the configuration was:
    Ti+2 = [Ar]4s2

    and not:
    Ti+2 = [Ar]3d2

    My reasoning was that if titanium itself, neutrally, is [Ar]4s23d2, then wouldn't, in this cation, taking away 2 electrons be more stable from the 3d sub-shell rather than the 4s sub-shell?

    Taking from the 4s sub-shell would leave 2 unpaired electrons in the 3d sub-shell, while taking from the 3d subshell would leave a complete electron pair in the 4s sub-shell, meaning more stability? Or is this thinking invalid?
    Last edited: May 30, 2012
  2. jcsd
  3. May 30, 2012 #2
    Even though 3d comes after 4s in order of filling the sub-shells, 4s has the higher energy level since n=4, and electron almost always comes out from the outermost energy shell.
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