Ionisation energy,Ionisation enthalpy of halogens
Ionisation energy (Ionisation enthalpy)-
Ionisation energy of all the halogens are very high because of small size and high effective nuclear charge of halogen atoms in
their respective period. However, Ionisation energy decrease on Moving down the group from fluorine to iodine which is due to increase in the size of the atom. Thus due to the low Ionisation energy of iodine, it is capable of forming I+ ion in it's compounds. Therefore, due to low IE of iodine it shows electro +ve or metallic character.