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Atomic Structure and periocity concept question

Why are the changes in election affinity as one goes down a group in the periodic table not nearly as large as variations in ionization energy. 
My book does not explain this concept very clearly.
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Think about what each one of these properties actually means.
Ionization energy is the tendency of a neutral atom to RESIST the loss of electrons. Or put another way, it is a measure of how much energy is needed to remove that electron.
Electron affinity is the energy given off when a neutral atom in the gas phase gains an electron to become a negative ion.
Now note that electron affinities are much smaller than ionization energies.  Some elements (like He, Be, N) have such stable electron configurations and such small affinities for extra electrons (they don't want them), that little or no energy is given off if and when these gain an electron to become a negative ion.  Since the values for EA are considerably smaller than those for IE, it is reasonable that the variations in EA are not as great as those for IE.