Trends in Electron Affinity

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TheresaDsilva4A
Posts: 53
Joined: Thu Jul 25, 2019 12:17 am

Trends in Electron Affinity

Postby TheresaDsilva4A » Sun Oct 20, 2019 1:27 pm

Is there a clear trend for electron affinity across a period/down a group (as for atomic/ionic radii)? Do you have any helpful tips for remembering the trend/exceptions to the rule? I struggled with this topic in AP chem, so I'd really appreciate any insight :) Thank you so much!

Yuri Lin 4H
Posts: 51
Joined: Sat Aug 17, 2019 12:15 am

Re: Trends in Electron Affinity

Postby Yuri Lin 4H » Sun Oct 20, 2019 2:06 pm

Electron affinity usually increases going up the periodic table and going left to right, but I believe there are a lot of exceptions to this (such as F having less electron affinity than Cl), especially moving horizontally.

For example, Be has less electron affinity than Li because beryllium's electron configuration is 1s^2,2s^2, and in order to add another electron to the atom, it would have to go into a 2p orbital, which is higher energy. On the other hand, Li has one less electron (1s^2,2s^1) and has room for one more electron in its 2s orbital, giving it more affinity to accepting another electron (higher electron affinity).

Another good example is C and N. N has one electron in each of its three 2p orbitals, so it is quite stable and therefore doesn't as readily accept electrons. On the other hand, C still has one completely unoccupied 2p orbital, so it will more readily accept an electron. Therefore even though N is further right on the periodic table than C, C still has a greater electron affinity than N.

All in all, I think having a good understanding of the relationship between orbital configurations and electron affinities is the best way to go. There aren't any fail-safe rules, unfortunately. Hope this helped at least a little!

Giselle Littleton 1F
Posts: 60
Joined: Wed Sep 18, 2019 12:20 am

Re: Trends in Electron Affinity

Postby Giselle Littleton 1F » Sun Oct 20, 2019 7:47 pm

As you go up and to the right, electron affinity increases as the atoms get more electronegative and are thus more likely to attract electrons. For example, oxygen is more electronegative and more likely to attract electrons than hydrogen. Oxygen is farther to the right in the periodic table and hogs the electrons in a chemical bond.

Shail Avasthi 3C
Posts: 86
Joined: Fri Aug 30, 2019 12:17 am

Re: Trends in Electron Affinity

Postby Shail Avasthi 3C » Sun Oct 20, 2019 8:59 pm

Electron affinity tends to increase as atoms get more electronegative, i.e. moving up and to the right on the periodic table.


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