Exceptions to electron affinity

[SophieCacdac_3H]

Hi, I'm looking through one of the UA's summary sheets and it says that the exceptions to electron affinity are group 2 because of the sublevel the last valence electron is placed in and group 15 because of interelectronic repulsions. I don't really understand the concept behind this. Could someone please explain in more detail?

[Aditya Narashim 1K]

Since group 2 has a full s orbital it has a lower electron affinity since a new electron would be added in a new subshell which wouldn't be very favorable. Additionally group 15 has a half full octet which has a special stability. Therefore these have a lower electron affinity than one may think.

[505989311]

The exceptions to electron affinity in Group 2 elements are due to the placement of the last valence electron in a higher energy sublevel (s), which makes it less likely for these elements to gain an additional electron. In Group 15, electron repulsion play a role; the added electron would enter a partially filled p sublevel, causing increased repulsions and making the process less favorable. This is because of the influence of electron configuration on electron affinity trends.