Electron gain enthalpy is the enthalpy Change take place when an electron is added to isolated gaseous atom . Electron gain enthalpy of halogens are highly negative because this process is exothermic in nature and large amount of heat is released . Fluorine is most electronegative element in the periodic table still it's electron gain enthalpy is less than Chlorine . Why Chlorine has High electron gain enthalpy than Flourine ? Size of fluorine is very small . So when an extra electron tries to attract toward this atom , their is large electron - electron repulsion take place between the outermost electrons and incoming electron . It becomes difficult for incoming electron to add up in the outermost shell . On the other hand , Chlorine is larger in size than flourine and when extra electron come in contact with this atom , Chlorine immediately tries to attract toward itself . Due to larger size , their is less electron - electron repulsion and it becomes easier fo...
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