2.67 part c) and d) [ENDORSED]

[Bianca Nguyen 1B]

In 2.67 part c), the solutions manual says that chlorine has a higher electron affinity than bromine and in part d), it says that lithium has a higher electron affinity than sodium. I just wanted to make sure my reasoning for this is correct. Is it because chlorine and lithium have smaller atomic radii since they have one less shell than bromine and sodium, and thus the electrons are closer to the nucleus?

[tatianatumbling_1J]

I believe your reasoning is right. That's the same explanation I would give; due to the smaller atomic radius, it takes more energy.

[Emma Leshan 1B]

Also, since chlorine and sodium have fewer electrons, there is less shielding, making the effective nuclear charge larger and making it harder to remove electrons.

[Mario Reyes 1C]

I'm confused by the reasoning. I thought electron affinity was dealing with adding electrons, not taking them away.

[Hannah Lee 1B]

Chlorine and lithium have higher electron affinity than bromine and sodium because as you go up a group, there is less shielding and you're closer to the nucleus, making it easier to add electrons. When an electron is added to a neutral atom, energy is released, and the harder it is to add electrons the smaller the net release of energy will be, therefore the value of electron affinity decreases down a group and increases across a period

[Chem_Mod]

Hannah's explanation is correct, and Mario is also correct. Electron affinity is the energy released when adding an electron.

Because I recognize that some students may struggle with the idea of shielding, here is an explanation on what it is:
viewtopic.php?f=23&t=31494&p=99740&hilit=electron+shielding&sid=7aaa87c777734fcade61f7bccb97cedc#p99740

Please let me know if you need further explanation!