Octet Rule [ENDORSED]

[Amoreno Section 1E]

What are the exceptions in the octet rule?

[Dabin Kang 1B]

One exception to the octet rule would be when atoms exceed their octet. Starting from phosphorus in period 3, atoms can utilize their d subshell in bonding.

[Paul Wong1B]

Another exception would be when when an atom has too little electrons in a compound. BeCl2, for example, is a compound in which the central atom does not possess an octet.

[Amy Wu 1D]

Do we have these exceptions to the octet rule only when we are more concerned with formal charge?

[Jordan Larrea 1E]

Do we have these exceptions to the octet rule only when we are more concerned with formal charge?

These exceptions have more to do with the fact that the d orbital is available, so it is used. Recall that the transition metals have a configuration one less than the row they're in, meaning that the metals in the n=4 row have the configuration of 3d. Because the 3d orbital exists in the third row, P, S, and Cl can use it. It's more to do with, it's there so we'll use it.

[Amy Wu 1D]

Do we have these exceptions to the octet rule only when we are more concerned with formal charge?

These exceptions have more to do with the fact that the d orbital is available, so it is used. Recall that the transition metals have a configuration one less than the row they're in, meaning that the metals in the n=4 row have the configuration of 3d. Because the 3d orbital exists in the third row, P, S, and Cl can use it. It's more to do with, it's there so we'll use it.

Ah, okay. Thank you for the clear explanation!

[404995677]

Hi I am still a little confused. So do the electrons go to to the 3d orbital for P, S, and Cl?

[605011646]

no, it only goes to 3p

[Ethan Mondell 1A]

Another exception to the octet rule would be radicals, compounds with unpaired electrons, meaning they would always have an odd number of electrons. Radicals, for the most part, are very temporary molecules and usually only form temporarily in some reactions.

[Chem_Mod]

Hey Everybody!
Great discussion on octets! There was a lot of stuff said in this thread so I'll summarize it and give some clarifications.
First, don't worry about radicals for now. Radicals will be discussed a lot more in later 14 series classes.
Second, exceptions to the octet rule can arise from your desire to minimize the number of atoms with formal charges (such as in the Lewis structure of ClO4-); however, exceptions to the octet rule don't ONLY arise from formal charge concerns.

These are the main exceptions to the octet rule:
-H and He only need to share 2 valence electrons to have a full octet.
-In certain compounds, such as BeCl2, Be only needs to share 4 valence electrons.
-In certain compounds involving the Boron group elements, such as BH3 and AlCl3, the central atom only needs to share 6 valence electrons.
-Typically, elements that are in the 3rd row or lower rows of the periodic table can have expanded octets. For example, in XeF4, Xe shares 12 valence electrons and in SF6, S shares 12 valence electrons.
Hope this helps guys! :D