Expanded Octet

[Angela Navas 4G]

When do we know to use the expanded octet rule. For example in SO4 (2-) both the four single bonded and 2 single 2 double bonded lewis structures are correct just one is more stable. Is there a way of knowing when we should use an expanded octet?

[francoisyap1I]

You would use it when there is a more stable Lewis structure available, as in SO4 (2-). More stable = less energy, which is what we want. While the four single bonded Lewis structure is possible, it's only possible in that single form. However, the 2 single 2 double bonded Lewis structure has resonance. Lewis structures that have resonance are also more stable, which is another clue that the expanded octet (2 single bond, 2 double bond) is the better choice.

[Patricia Zhao 1C]

Use expanded octet whenever possible (third shell or greater) in order to lower formal charge values.

[joannali1027]

So by third shell should we just assume that they all can have an expanded octet? Also, can there be expanded octets before n=3?

[Samantha Rundle 3K]

Why can P, S, and Cl accommodate more than 8 valence electrons? I know the course reader says they have d-orbitals in the valence shell that accommodate additional electrons, but I'm not sure I understand what that means because their electrons do not occupy a d-orbital. Can somebody please clarify?


Thank you!

[Shrita Pendekanti 4B]

It helps to think of it like they have d-orbitals "available" since they are in the third energy level (n=3 so l=2), but they just don't need to occupy these orbitals given the number of electrons they have.

[Caroline Chen 2A]

I still don't understand. Why don't they need to occupy these orbitals given the number of electrons they have?

[joannali1027]

Is there a limit to how many electrons an atom can accommodate? Say, the sulfur atom has an electron configuration of and 2 empty spaces in its d-orbital. Does this mean sulfur can thus accommodate 2 more electrons/one extra loan pair? Can it accommodate more? If so, why is that?

[104422816]

Also, is it only Hydrogen and Helium that can have less than an octet?

[Caroline Chen 2A]

Also, is it only Hydrogen and Helium that can have less than an octet?

I don't know how to answer Joanna's question, but I believe lithium, beryllium, and boron also have less than an octet even when bonded with other atoms.