Electron Affinity

Is the energy released when an electron is added to an atom.

M_(g) + 1e^– ––> M^–_(g)

Electron affinities tend to follow the trends in ionization energies. If the ionization energy is large, the electron affinity is large (exothermic). It makes sense the electron affinity should increase going across a period since the effective nuclear charge increases. EA decreases going down a grounp. As the distance from the nucleus of the shell the electron is beng added to increase the energy released also decreases.

Nitrogen is smaller than expected because it has a half-filled subshell and adding an electron means there will be some electron-electron repulsions incountered. So the energy release is small, in fact it is very close to zero.