ELECTRON AFFINITY OR GAIN ENTHALPY

ELECTRON AFFINITY OR GAIN ENTHALPY 

The amount of energy released or absorbed when an electron is  added to the valance shell of is isolated gaseous atom know as electron affinity,,,,,,,,,

X(g) + e⁻ → X⁻(g) + energy

mostly energy of release in the process of  1 E.A. so it is exothermic    - ΔHmost imp.    

Energy involved in E.A. to convert nutral atom to anion = Energy absorbed to removed electron from anion 

SECOND ELECTRON AFFINITY -

SECOND ELECTRON AFFINITY is an endothermic process that is energy has to give introduce the second electron in an anion because of repulsion between the negative charge on anion and 2 E.A. is always negative ... 

FACTOR AFFECTING OF E.A.
ATOMIC SIZE -Electron affinity      a    1/ Size of the atom 

when stomic size is increses then E.A. decreses 

2)SCREENING EFFECT Electron affinity a  1/ screening effect when the screening effect is increasing then electron affinity is decreased MOST IMP.-1) stability of complete field or half field orbital-

E.A. of half feild and full feild less or zero 

EX. He, Ne, Ar E.A. is zero because of full-field electronic configuration,,,,,,

Ne -1s²2s²2p⁶ 

Ar-1s²2s²2p⁶3s²3p⁶ 

both are full electronic configuration then E.A is zeroEX- N, P E.A is a  very less because of half field configuration,,,,,,,,,

N-1s²2s²2p³

P-1s²2s²2p⁶3s²3p³

both are half field electronic configuration then E.A. is very less 
IN A PERIOD 1) In a period the E.A. left to right is increases- Ex. in a second period-
Li              Be              B           C           N              O              F             Ne    2s1,                2s²                  ,2s2 2p1      2s2 2p2          2s2 2p3            2s² 2p⁴            2s2 2p5           2s²2p⁶ 
E.A. order -Ne    < N <    Be <       B  < Li    <   C  <     O  <    F      in a period left to right E.A. is increasing but in case of   Ne    N     Be      B    Li group number is a full field and half field electronic configuration then half field or full field is zero are very less than in the order in  2 periods Ne is very less E.A. to another element IN GROUP-1)group number 17--- Cl        F        Br      I      in down the group E.A. is decreased    Cl   <     F    <    Br  <    I      Cl is highest E.A. in hole periodic table and O  is lowest E.A.,,,,,,,,,,,,,,,,,,,,