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Electron affinity

  1. Apr 20, 2004 #1
    I have a problem with MgO(s).

    Mg(s) → Mg(g) Heat of sublimation = +148 kj

    ½O2(g) → O(g) Bond dissociation = +249 kj

    Mg(g) → Mg2+(g)+ 2e- IE1+IE2= +2201 kj

    O(g)+2e- → O2- EA= +737 kj

    look at the EA in peiodic table O(EA= -141 kj).
    When O charged 2e- it seems to be like F(EA=-328 kj) charged 1e-.
    it should be - not +.
    but Why EA of O=+737kj ?
     
  2. jcsd
  3. Apr 21, 2004 #2
    the first electron affinity is exothermic and after always endothermic
     
  4. Apr 21, 2004 #3
    thank you.
     
  5. Feb 21, 2010 #4
    But, I would like to know why it is always exothermic and then always endothermic, I am trying to find the logic behind, but I cannot!!!!!
     
  6. Feb 22, 2010 #5

    DrDu

    User Avatar
    Science Advisor

    How do you bond an electron to a species that is already negatively charged?
    Formally multiply charged ons like O^{2-} exist only in solids (or liquids) where they are surrounded by positive charged ions which provide a potential well to stabilize bonding of the seconde electron.
     
  7. Feb 22, 2010 #6
    Oh Ok, Thank you very much!!!
     
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