## Expanded Octet

Angela Navas 4G
Posts: 6
Joined: Fri Sep 26, 2014 2:02 pm

### Expanded Octet

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
Posts: 1
Joined: Fri Sep 26, 2014 2:02 pm

### Re: Expanded Octet

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
Posts: 3
Joined: Fri Sep 26, 2014 2:02 pm

### Re: Expanded Octet

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

joannali1027
Posts: 21
Joined: Fri Sep 25, 2015 3:00 am

### Re: Expanded Octet

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
Posts: 22
Joined: Fri Sep 25, 2015 3:00 am

### Re: Expanded Octet

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
Posts: 22
Joined: Fri Sep 25, 2015 3:00 am

### Re: Expanded Octet

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
Posts: 20
Joined: Fri Sep 25, 2015 3:00 am

### Re: Expanded Octet

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

joannali1027
Posts: 21
Joined: Fri Sep 25, 2015 3:00 am

### Re: Expanded Octet

Is there a limit to how many electrons an atom can accommodate? Say, the sulfur atom has an electron configuration of $3s^23p^4$ 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
Posts: 17
Joined: Fri Sep 25, 2015 3:00 am

### Re: Expanded Octet

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

Caroline Chen 2A
Posts: 20
Joined: Fri Sep 25, 2015 3:00 am

### Re: Expanded Octet

104422816 wrote: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.