Octet Rule

[Carolina Lechuga]

Hey, so my TA told us that following the octet rule is more important than getting a low formal charge. This is one of the biggest mistakes I did on the midterm so what exactly are the exceptions to the octet rule??

[Raphael_SanAndres3C]

Elements in the third period can utilize the d oribital, thus allowing it to have more than an octet. However, you do not want to not have at least an octet with all your elements (with the exceptions being H, He, Li, and Be).

[taline_n]

When drawing lewis structures, the first rule to fulfill is the octet rule. Formal charges come after, as a way to guide you to the correct structure by adding and rearranging double/triple bonds to lower the formal charges of each atom. However, the octet rule comes first. Each atom must have an octet before you consider formal charge.

Another thing to consider is that although many elements can have an expanded octet, many other elements, like Nitrogen, cannot. Drawing more than 4 bonds for a single Nitrogen atom is incorrect, no matter what the formal charge may be. So, it's better to have a nonzero formal charge on an atom than too many / too few electrons.

[dgerges 4H]

Sulfur, phosphorus, silicon, and chlorine are common examples of elements that form an expanded octet which means they can have more than the usual 8.

[Sameen Mahmood 3D]

Well keep in mind that there are elements that break the octet rule, not just elements in period 3 or greater that can have expanded valence (because they can use the d orbitals) but also elements such as Boron or Aluminum which generally only form three bonds. It wouldn't be good to have a boron with a negative formal charge.

[Nathan Tran 4K]

Another common exception to the octet rule that we don't often talk about is hydrogen just because it's so intuitive to make a single bond without completing its octet. It's one we don't think about often breaking the octet, but one that does nonetheless.

[Max Kwon 1J]

I would say formal charges are more important at period 3 and on, as they can use the d-block for electrons. Also, group 13 are exceptions you have to look out for, as well as hydrogen, helium, lithium, and beryllium as they can't get to 8 and are fine with 2 for a full shell. The octet rule is still useful but there are expanded octets you have to look out for.