Exercise 2.67

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Johana Jeon 1A
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Exercise 2.67

Postby Johana Jeon 1A » Sun Jul 09, 2017 6:12 pm

In 2.67: Which element of each of the following pairs has the higher electron affinity:
a) oxygen or fluorine
b) nitrogen or carbon
c) chlorine or bromine
d) lithium or sodium

For b, why isn't nitrogen higher?
Doesn't electron affinity increases upward for the groups and from left to right across periods of a periodic table?

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Re: Exercise 2.67

Postby Gwyndolyn » Sun Jul 09, 2017 8:53 pm

Electron affinity is less periodic, and therefore doesn't always follow a specific trend, but generally the elements in the top right, group 17, have a high affinity for electrons.
In this case, I think that carbon has a higher e- affinity than nitrogen because carbon has a half-filled "p" subshell, which gives it more stability and therefore a higher affinity for electrons.

Chels Zh 1D
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Re: Exercise 2.67

Postby Chels Zh 1D » Tue Jul 11, 2017 9:13 pm

I am still confused while I checked the chart in course reader page 70, it shows that carbon has an energy of +122kJ/mol, while nitrogen has an energy of -7kJ/mol. But why is it true according to the trend of electron affinity?

Savanna Gharibian 1A
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Re: Exercise 2.67

Postby Savanna Gharibian 1A » Tue Jul 11, 2017 9:28 pm

Could it be that it's just an exception? I don't remember going over anything of the such in class but maybe I just missed it.

Jana Sun 1I
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Re: Exercise 2.67

Postby Jana Sun 1I » Fri Oct 27, 2017 12:36 am

Actually, since nitrogen has a perfectly half filled p-orbital, it is more stable than carbon. Meanwhile, carbon only has two half filled p-orbitals out of three. Therefore, it wants another electron more than nitrogen does in order to fill half of its p-orbital completely; so, its electron affinity is higher. Looking at the comments in this post (viewtopic.php?f=25&t=22591) might also help!

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