Octet Rule Exceptions

[Lucy Weaver 1K]

I know in class we were taught that H,He, Li, and Be are exceptions to the octet rule as well as group 13 elements, but are there any otheres? in the sapling homework I learned that phosphate is also an exception because it can have 10 (5 shared) if it makes the formal charge lesser. I'm curious to what the other exceptions are if anyone knows.

Thanks in advance!

[HannahRobinson3L]

Hi! Similar to P, S and Cl can accommodate more than 8 valence electrons. This is because atoms in period 3 or higher have d-orbitals that accommodate these elections. There are also other exceptions that Dr. Lavelle mentioned in lecture such as radicals that have unpaired electrons, and lewis acids such as BF3 where some atoms have less than 8. If you need more clarification, it might be good to watch the lecture from 11/4 one more time to review the exceptions.

[isha dis3d]

I believe that any elements past the atomic number 10 can have an expanded octect. This is because we see that when there are 5 or 6 groupson the central atom, d- orbitals are involved which allow octects to expand.

[Veronica Macias 3K]

In a step-up session, I was told anything after period 2 can expand its octet and all the elements in group 13 only need 6 valence electrons.

[AlbertGu_2C]

If somebody could help me make a list of all of the exceptions for this midterm, that would help a lot. Right now I have the first four elements, elements past period 3 can exceed, and group 13 only need 6. Thanks!

[Jaden Joodi 3J]

Sulfur and Chlorine are the only two exceptions I believed you did not mention. Like Phosphorus, these are able to accommodate more than 8 valence e-. This is due to the 3d block being able to be used to store extra electrons

[Mari Williams 1K]

Are we expected to memorize the exceptions for the midterm?

[Khushi_Gupta_1A]

There are three general exceptions to the octet rule:
1. Having too many electrons for an octet. This can be done when an element's valence shell has access to the d-orbitals in the third energy level and beyond. There needs to be enough orbitals to accommodate the extra electrons. I believe chlorine, silicon, phosphorus, and sulfur are common examples of elements that can have an expanded octet.
2. Another exception to the octet rule can be seen when there's too few electrons (electron-deficient). Hydrogen, beryllium, and boron have too few electrons to form an octet.
3. The last exception would be free radicals—when there's an odd number of electrons in the valence shell, which means there's at least one unpaired electron. ( an example would be elements like Nitrogen)

[lwon Dis2I]

I am slightly confused about drawing lewis structures, and specifically the octet rule. Do elements with 1 or 2 valence electrons have to fill an octet? For example, when drawing out a compound that contains the element Na (which has one valence electron), is it ever possible for it to fill the octet?

[Sophia Wendin 3L]

I am slightly confused about drawing lewis structures, and specifically the octet rule. Do elements with 1 or 2 valence electrons have to fill an octet? For example, when drawing out a compound that contains the element Na (which has one valence electron), is it ever possible for it to fill the octet?

I think Na usually loses an electron and becomes a cation that can form an ionic bond!

[Emmeline Phu 1G]

Hi! The general octet rule exceptions would be group 13 elements which usually only need 6 electrons to be stable (B, Be, etc). Elements such as H, He, Li need only 2 electrons be to be stable. As for an expanded octet, or elements that are able to accommodate more than 8 electrons, they have to be in period 3 or greater. Starting from n=3, the d-orbital is now included meaning that the elements are able to accommodate more than 8 electrons from only the s-orbital and the p orbital. Hope this helps! :)

[clairehathaway 2J]

Hi! The general octet rule exceptions would be group 13 elements which usually only need 6 electrons to be stable (B, Be, etc). Elements such as H, He, Li need only 2 electrons be to be stable. As for an expanded octet, or elements that are able to accommodate more than 8 electrons, they have to be in period 3 or greater. Starting from n=3, the d-orbital is now included meaning that the elements are able to accommodate more than 8 electrons from only the s-orbital and the p orbital. Hope this helps! :)

So just to make sure, BH3 would be more stable with the boron only having 6 electrons (from the bonds) instead of 8 electrons (3 bonds and 1 lone pair) right?

[Britney Tran IJ]

https://courses.lumenlearning.com/bound ... ctet-rule/

this is a good resource that summarizes all of the exceptions!!

[Binyu You]

I believe B is an exception where when 6 electrons can fill up the octet. Hydrogen is an exception were it only need two electrons to complete the octet. P,S, and Cl are exceptions where they can have more than 8 electrons in the octet.

[Norah Gidanian 3D]

I believe that B and Al dont need an octet as well.

[Lilly Catarozoli 1B]

P, S, and Cl, are elements that can have an expanded octet.

[John_Tran_3J]

From my memory, I believe Phosphorus, Sulfur, and Chlorine have expanded octets, meaning they can contain more than 8 valence electrons. There are also molecules that don't have to abide by the octet rule, they are known as Hydrogen and Helium.

[Xavier Herrera 3H]

The first four elements, H, He, Li, and Be only need two electrons to fill their orbital since they bond to try to fill the 1s orbital. The elements in group 13 only need 6 electrons, and elements in period 3 and lower on the periodic table can have more than eight electrons in their outer shell due to the d orbital.

[Zainab Jamali 1H]

Thanks for asking this question! This thread is very helpful :)

[Yolanda_Xing_3A]

I think I saw one YouTube video saying elements after #15, P, can form exceptions of octet rule. And so does the first few elements.

[Bai Rong Lin 2K]

I think I saw one YouTube video saying elements after #15, P, can form exceptions of octet rule. And so does the first few elements.

This is very helpful. thank you!