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    I was given an exam question concerning election configurations and after checking the mark scheme i found it said that the answer that i gave was to be rejected.

    The question asked me to fill to complete the electron configuration of a copper atom
    they complete the electron configuration up to  3_p
    My answer was  3d^94s^2, the mark scheme gave the answer 3d^1^04s^1 is 4s filled first.
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    Yes, in Copper and Chromium (the two exceptions) the 4s is filled in first. This is when, in chromium it ends in 3d54s1. I think, this is what i remember.

    This is due to it being more stable when there are 5 pairs of electrons in the 3d orbital, as opposed to 4 pairs and an odd one.
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    (Original post by Thomas...)
    Yes, in Copper and Chromium (the two exceptions) the 4s is filled in first.
    The two you need to know about for A level, that is.
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    (Original post by BJack)
    The two you need to know about for A level, that is.
    Ok ok ok. I have been out-shone.
    Ha, I was just regurgitating what I remember from last year! Thanks for the edit.
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    (Original post by Thomas...)
    Yes, in Copper and Chromium (the two exceptions) the 4s is filled in first. This is when, in chromium it ends in 3d54s1. I think, this is what i remember.

    This is due to it being more stable when there are 5 pairs of electrons in the 3d orbital, as opposed to 4 pairs and an odd one.
    Right i see thank you very much for your help
 
 
 
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