Extended Octet for Sulfur


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Eileen Quach Dis 2A
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Extended Octet for Sulfur

Postby Eileen Quach Dis 2A » Mon Nov 02, 2020 1:32 pm

I'm a bit confused on why Professor Lavelle said that sulfur has an extended octet, or that it can have more than 8 valence electrons in the example with the sulfate ion.

Samantha Pedersen 2K
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Re: Extended Octet for Sulfur

Postby Samantha Pedersen 2K » Mon Nov 02, 2020 1:51 pm

Sulfur can have an expanded octet because it is in Row 3 of the periodic table, meaning that the quantum number n is equal to 3. When n=3, l can be 0, 1, or 2 according to the rules for quantum numbers. This means that elements in Row 3 have the S, P, and D subshells available to them to hold electrons. The S and P subshells provide 4 orbitals that can hold 2 electrons each (this is why we have the octet guideline), and the D subshell provides 5 additional orbitals that can hold 2 electrons each (this is why some elements can have more than 8 valence electrons).

This explanation also means that elements like silicon, phosphorus, and chlorine can have more than 8 valence electrons because they are in Row 3 of the periodic table too. I hope this helps!

Nadya Higgins 3F
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Re: Extended Octet for Sulfur

Postby Nadya Higgins 3F » Mon Nov 02, 2020 1:56 pm

I believe this has to do with how its valence shell has enough orbitals to accommodate more than 8 electrons. From what I understand, sulfur's electron configuration is 1s^2(2s^2)(2p^6)(3s^2)(3p^4), and at the n=3 level, the d subshell exists (I think because l=0 to 2) allowing more electrons to occupy its empty orbitals. However, I may be wrong since I'm also not fully clear on this question either, and will be happy to see if anyone else can explain in more detail!

sophie esherick 3H
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Re: Extended Octet for Sulfur

Postby sophie esherick 3H » Mon Nov 02, 2020 2:45 pm

Hi! Elements in periods greater than period 3 on the periodic table have a d orbital available with the same energy quantum number. Atoms in these periods may follow the octet rule, but there are conditions where they can expand their valence shells to accommodate more than eight electrons.
Sulfur and phosphorus are common examples of this behavior. Sulfur can follow the octet rule as in the molecule SF2. Each atom is surrounded by eight electrons. It is possible to excite the sulfur atom sufficiently to push valence atoms into the d orbital to allow molecules such as SF4 and SF6. The sulfur atom in SF4 has 10 valence electrons and 12 valence electrons in SF6.


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