Electron affinity

  • Thread starter osaka
  • Start date
  • #1
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Main Question or Discussion Point

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 ?
 

Answers and Replies

  • #2
308
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the first electron affinity is exothermic and after always endothermic
 
  • #3
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thank you.
 
  • #4
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the first electron affinity is exothermic and after always endothermic
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!!!!!
 
  • #5
DrDu
Science Advisor
6,032
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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.
 
  • #6
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Oh Ok, Thank you very much!!!
 

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