Why is the first electron affinity exothermic?

1 Answer
Dec 7, 2015

Sometimes it is; especially for elements to the right of the Periodic Table.


Electron affinity is the enthalpy associated with the reaction:

#M(g) + e^(-) rarr M^(-)(g)#

We would expect this enthalpy to increase across a Period from left to right (because of the increased nuclear charge), and to decrease down a Group, as the nuclear charge is insulated by intervening electron shells.

Metals tend to have low electron affinity, as these are reducing species.