electron affinity

[osaka]

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 ?

[garytse86]

the first electron affinity is exothermic and after always endothermic

[osaka]

thank you.

[abiir0611]

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!!!!!

[DrDu]

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.

[abiir0611]

Oh Ok, Thank you very much!!!