Expanded octet

[Sarah Salam 1J]

Do we always make an expanded octet if we can? Also, the professor explained why they are ok, but I didn't fully understand the explanation. What does it have to do with orbitals?

[505352202]

No, we don't always make expanded octets even if they are possible on our lewis structure. Sulfur was the example given in the lecture, but other elements with an expanded octet include Chlorine, Silicon, and Phosphorus. All these elements contain d-orbitals, and that's why they can have more than 8 electrons.

[Sarah Salam 1J]

Oh, that clears it up, thank you!

[Sunny Wu 3A]

To add on, this might help:

1) The central atom with an expanded octet MUST have an atomic number larger than 10
(beyond neon).
2) Extra electrons should be first placed on the outside atoms. After the outside atoms have
fulfilled the Octet Rule, and there are still extra electrons, start with placing them as lone
pairs on the central atom. If the central atom does not have a positive formal charge, do not
go any further. You have the correct Lewis structure. Only if the central atom has a positive
charge should you move a lone pair from the outside atoms to share.

As to why they occur, molecules can achieve a lower energy level in some cases (which is favorable) if the electrons in the central atom can "fill up" the available d orbitals to form covalent bonds.

[DavidTabib 3H]

P, S, and Cl are elements that are able to have an expanded octet