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Hypervalent oxygen

  1. Jul 15, 2015 #1
    I know that it is possible for 2 H2O molecules to gain and lose electrons. This reaction looks like this:

    2 H2O -> H2O+ + H2O-

    This causes 1 of the oxygen atoms to be hypervalent since it now has 9 electrons. The other oxygen has only 7 electrons. The electron on the hypervalent oxygen came from 1 of the other oxygen's lone pairs.

    Obviously this ionic water is not stable.

    But how is this ionic water possible when it violates 1 of the general rules in chemistry which is that hypervalency starts in the 3rd period not group 16 of the 2nd period.
     
  2. jcsd
  3. Jul 15, 2015 #2
    Is this really true ? Because I have never seen anything like this, rather i have seen this
    2H2O = H3O+ + OH-
    Pls. Read the equal to as a reversible arrow.
     
  4. Jul 15, 2015 #3
    Yes under certain conditions H2O+ and H2O- can form
     
  5. Jul 16, 2015 #4

    DrDu

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    Science Advisor

    Hypervalency not being possible in 2nd row elements is nowadays known to be a fairy tale, which nevertheless is going on to get told to high school students.
    Nevertheless, I don't think that this reaction happens. In gas phase, H2O- is only marginally stable. The electron is bound by the dipole moment of the water molecule and is spread out over a large area. It does not resemble a valence electron at all. On the other hand, it cost's a lot of energy to ionize H2O to H2O+, so this reaction is not feasible in the gas phase.
    In solution, H2O- doesn't exist. Rather, there exist a solvated electron for a short time, which rapidly reacts under the formation of H2 and OH-. Again, energetics isn't favourable.
     
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