Electron Affinity - P, Na, Ar

[Michelle Pham_3H]

In Test 3, there was a question that asked us to put several elements in order of decreasing electron affinity. Using the general guideline that electron affinity increases across a period and decreases down a group, I put P, Na, and Ar into the order Ar, P, and Na. The correct answer was P, Na, Ar. Why does Ar have the lowest electron affinity? Thanks in advance!

[Vincent Chiang 1L]

According to my TA, noble gases have very low electron affinities.

[Erik Khong 2E]

Ar has lower electron affinity because it's a noble gas with 8 full valence electrons. It would require energy to add another electron since its full and repulsion will play a factor.

[Salman Azfar 1K]

A good thing to remember is that F has the highest electronegativity. That means the stuff past it on the right (Noble gases) has lower values, and Noble gases have their octets and actually really don't want electrons.

[MichelleKaku1H]

Yes! Just remember that noble gases are an exception when it comes to electron affinity!