[عاطف خليفة]

* 3- Electron affinity :

“The amount of energy released when an extra electron is added to a neutral gaseous atom”.

a) In periods

- The electron affinity increases as the atomic number increases

exception

-

The filled or half- filled orbital give the atom some stability so it is difficult to attract new electron and the electron affinity decreases

(As in 4Be = 1S2,2S2 , 7N = IS2,2S2,2p3, 10Ne =lS2,2S2,2p6)

b) In groups:

-

The electron affinity decreases as the atomic number increases due to increasing atomic radius increasing the repulsive force between the electrons and decreasing attraction force .

exception

Electron affinity of fluorine is less than that of chlorine due to the smallest Of the radius of flourine which causes high repulsive force between 9 electron of flourine.