Electron configurations with completely full shells and half-full shells exhibit an increased stability over other electron configurations. Therefore, nitrogen (1s22s22p3), which already has a half full 2p shell, will not want to eliminate the stability of a half-full shell by gaining an electron. Therefore, it has a lower electron affinity than expected by electronegativity alone. On the other hand, carbon (1s22s22p2) is one electron away from the stability of a half-full shell; therefore, it has extra "incentive" to seek out an extra electron and obtain a half-full 2p shell. So, carbon exhibits a higher electron affinity than expected by electronegativity alone. In much the same way, oxygen (1s22s22p4) will want to get rid of an electron in order to obtain a half-full 2p shell, so its ionization potential will be lower than expected.
g english: High spin/low spin in transition metal complexes is dictated by the ligands as well as in which row the metal sits. But, what does this have to do with the question?