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    ionisation values michellemcc98

    Can somebody please help me answer this : why are the 4th and the 12th ionisation values so high? Why does sulphur have a lower 1st ionisation value than oxygen or phosphorous?

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      For the 4th and 12th element, if you look at their electronic configurations;

      4: 1S2, 2S2

      12: 1S2,2S2,2P6,3S2

      In both of these cases the sub-levels are all filled, which gives them greater stability, which means higher values of ionisation.

      As for sulfur, its similar.

      Sulfur is 16, so the config is : 1S2,2S2,2P6,3S2,3PX2,3PY1, 3PZ1

      Phosphorous before it, has 15, : 1S2,2S2,2P6,3S2,3PX1,3PY1, 3PZ1

      The important thing to look at is the "3PX" sub level, in Phosphorous, all the "3P" sub levels are half-filled (Half-filled gives greater stability).

      Whereas in Sulfur, the "3PX" sub level has an extra electron, meaning the 3P sub level is just over half-full.

      In summary, if an element has all of its sub-levels half-filled or filled then it will have greater stability, and therefore higher ionisation values.

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