why the electron affinity of phosphorus has negative sign with it....which factor is implement on it? and why the electron affinity of nitrogen is indicated by positive sign?
Electron configurations with completely full shells and half-full shellsexhibit an increased stability over other electron configurations. Therefore, nitrogen (1s22s22p3), which already has a half full 2p shell, will not want toeliminate the stability of a half-full shell by gaining an electron. Therefore, it has a lower electron affinity than expected by electronegativity alone. For Phosphorus the 3p level is exactly half filled (note that half filled and fully filled orbitals are more stable configuration), so for accepting one more electron by phosphorus (that is what electron affinity is) it will diturb the stable electronic configuration and therefore the electron affinity for P is less than the N.