Expanded Octets [ENDORSED]

[Rohita Thammineni 2D]

Can someone clarify when expanded octets are acceptable/preferred over normal octets? For example, I was trying to create a Lewis structure for one of the problems in the homework, but I received feedback that it wasn't the most preferred structure. Then, I created a structure with an expanded octet that had more formal charges of 0 in comparison to the structure with the normal octet, and it was correct. Do we always go with the structure with the more favorable formal charge even if it doesn't follow the octet rule? I'm just confused about where the exceptions to the octet rule start on the periodic table and why they exist...

[Jayden Arevalo 2B]

Hi Rohita, exceptions to the Octet rule begin in the 3rd energy level/period and beyond, since they are capable of holding more than 8 electrons. We always want to find the structure with the least amount of formal charges, as it results in an overall more stable compound.

[Robert Nguyen 14B-3E]

After the 3rd row of the periodic table, the d suborbital is available to an atom, which allows the atom to have more than 8 electrons (which was the limit of the 2 of the s and 6 of the p). So the octet rule can be broken in cases where the atom is in the 3rd row or below, if it results in less formal charges.

[Rachel Fox - 3F]

There are exceptions to the octet rule in elements starting in the 3rd energy level because then the quantum number l can be 0, 1, or 2 which corresponds to the s, p, and d orbitals. During bonding, elements such as sulfur can have more electrons because the 3d state can be used for bonding. Thus, for atoms like sulfur, the 3d orbital can be used when there is the expanded octet because the atoms are capable of holding more electrons. The expanded octets are preferable over the non expanded octet when the formal charge is closer to 0, which indicates more stability.

[Emily2J]

The Octet rule begins to be less used in the 3rd energy period and beyond, because they are able to hold more than 8 electrons. This is when the formal charge is important. The lower the formal charge the more stable the molecule.

[Jacqueline Duong 1D]

Hi!
I wanted to piggyback off Rohita's post and ask a related question about formal charges. I am a little unclear on how and when we would apply formal charges in order to determine what would be the preferred structure. I am okay with the formal charge calculation for each individual atom, I'm just a bit confused on the application.

Thanks in advance!

[Andrew Nguyen 1E]

To Jacqueline,

I would say to always find formal charges to find the most stable Lewis structure (where as many charges are 0), except for molecules we already know like H2O or CO2. This is because questions usually want Lewis structures in their most likely state, which is their most stable.

[Emily Widjaja 3A]

Hello,

I think at the third energy level, the atoms are starting to have d orbitals. So "extra" electrons can be placed in the d orbitals, leading them to have expanded octets.