I have found that as we go down the group 18(noble gases), the electron gain enthalpies of the elements become less and less positive in general. But i think they should be more and more positive since this is the general trend in the periodic table. Can you please help me sort out this confusion?
Noble gases have large positive electron gain enthalpy because electron has to enter next higher principle quantum level leading to a very unstable electronic configuration.
The electron gain enthalpy decreases down a group as increase in the size of the atom and also the added electron would be further away from the nucleus.
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