Exceptions to Ionization energy trends?

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Ishan Ayyala 2K
Posts: 31
Joined: Fri Sep 25, 2015 3:00 am

Exceptions to Ionization energy trends?

Postby Ishan Ayyala 2K » Fri Oct 09, 2015 10:37 pm

Ionization energy increases across a period due to increasing nuclear charge which leads to outer electrons being held onto very tightly. I was wondering then why the ionization energy decreases when comparing Be and B, and N to O which goes against the aforementioned principle?

Bryan Nguyen 1A
Posts: 20
Joined: Fri Sep 25, 2015 3:00 am

Re: Exceptions to Ionization energy trends?

Postby Bryan Nguyen 1A » Sat Oct 10, 2015 12:16 am

I'm not great at explaining things but the electron configuration of beryllium is 2s2 and of boron is 2s2 2p1. Electrons in the p-orbital have higher energy than electrons in the s-orbital. Higher energy means that it would easier to remove an electron, so it would be easier to remove the electron from the 2p-orbital of boron than it would to remove one from the 2s-orbital of beryllium.

The electron configuration of nitrogen is 2s2 2p3 and of oxygen is 2s2 2p4. Nitrogen has 3 unpaired electrons in the 2p-orbital while oxygen has 2 unpaired electrons and 1 paired electrons in the same orbital. The paired electrons in the 2p-orbital of oxygen are constantly repulsing against each other, increasing their energy and making it easier to remove an electron.

Generally, groups 2 and 15 have a slightly higher ionization energy than groups 13 and 16 respectively because of these two concepts.

Sandeep Gurram 2E
Posts: 42
Joined: Fri Sep 25, 2015 3:00 am

Re: Exceptions to Ionization energy trends?

Postby Sandeep Gurram 2E » Sat Oct 10, 2015 12:28 am

Bryan did a great job of explaining. Basically, there is a greater electron-electron repulsion force within the oxygen atom than there is within the nitrogen atom because the eighth electron in oxygen is paired with an electron that is already occupying an orbital. This repulsion of electrons in the same orbital raises the energy of the oxygen atom and makes it slightly easier to remove the electron from the oxygen atom. Hope that clears things up!

Ishan Ayyala 2K
Posts: 31
Joined: Fri Sep 25, 2015 3:00 am

Re: Exceptions to Ionization energy trends?

Postby Ishan Ayyala 2K » Sat Oct 10, 2015 2:29 pm

Cool that makes sense. Thanks both of you for your help!


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