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How many electrons can sulfur take?

Obviously sulfur has 6 electrons in its outer shell but how many can it accept? Ive seen sources online say 6 more electrons to form 6 covalent bonds but what about dative bonds? Would 6 still be the maximum then? My initial thought was that it might be able to take 18 since the 3rd shell is 3s2 3p6 3d10 but then 4s fills up before 3d so that probably isn't right? Thank you!!
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Original post by apolaroidofus
Obviously sulfur has 6 electrons in its outer shell but how many can it accept? Ive seen sources online say 6 more electrons to form 6 covalent bonds but what about dative bonds? Would 6 still be the maximum then? My initial thought was that it might be able to take 18 since the 3rd shell is 3s2 3p6 3d10 but then 4s fills up before 3d so that probably isn't right? Thank you!!


Sulfur gains 2 more electrons to make a stable sulfur molecule with a full outer shell. The ionic equation is Su2- + 2e- ----> Su
(edited 1 year ago)
I would say that it is extremely unlikely if not impossible for a sulfur atom to end up with an electronic configuration of 3s2 3p6 3d10, that would mean it would have 28 electrons and a -12 charge, I doubt a nuclear charge of +16 could hold 28 electrons in place!!!!! Sulfur can have an expanded valency shell and hold up to 12 electrons in molecules such as SF6 (https://www.science-revision.co.uk/A-level_exceptions_to_the_octet_rule.html)
Original post by apolaroidofus
Obviously sulfur has 6 electrons in its outer shell but how many can it accept? Ive seen sources online say 6 more electrons to form 6 covalent bonds but what about dative bonds? Would 6 still be the maximum then? My initial thought was that it might be able to take 18 since the 3rd shell is 3s2 3p6 3d10 but then 4s fills up before 3d so that probably isn't right? Thank you!!


SF6 has S with 12 e- in it's outer shell. I don't think it can have more. Or at least I hope to God almighty that someone hasn't persuaded it to have more. The fools. Meddling with nature itself.
The number of bonds sulphur can form is a dependent on the associated enthalpy changes of bond formation. The explanation I've heard at undergrad level is based on formal oxidation states and ionisation energies.

Say sulphur forms a bond with an atom more electronegative than it like oxygen. Oxygen is more electronegative, so both of the electrons in the S-O bond are polarised towards the oxygen atom. Since the bond was formed using one electron from S and one from O, this is the same as saying oxygen has basically taken an electron from S, oxidising it. This is the basis of the formal oxidation state of an atom in a molecule. If we view bond formation like this, the number of possible bonds gets much easier to explain.

How do we express the energy necessary to oxidise a species? Ionisation energy. What you will probably already know is that ionisation energies are reasonably small until you start taking them from a lower shell. Sulphur is group 6, so it has 6 valence electrons in its outer shell. If you attempt to remove these electrons, the ionisation energy will progressively increase (as you're trying to remove electrons from an increasingly positive sulphur), but it won't get excessively massive until you try to remove the 7th electron, which is in the shell below, much closer to the nucleus.

Putting everything together:

Every time sulphur forms a bond to an atom more electronegative than itself, we 'oxidise' it. We aren't fully removing the electron, but we're pulling the electron away from sulphur, so ionisation energy is a reasonable approximation for the energy required to do this. To form a bond, the stabilisation that bond formation provides (i.e., the strength of the bond) must be large enough to compensate for this 'ionisation energy', making the overall bond forming process energetically favourable.

We know that we can oxidise the sulphur 6 times without stupidly high ionisation energies, so if our bonds are strong enough, stabilisation from bond formation will compensate for the ionisation energy and make the formation of 6 bonds energetically favourable. When we try to pull another electron away by forming a 7th bond, our ionisation energy skyrockets and essentially no bond you could make would compensate for it, so the overall process of forming a 7th bond is energetically unfavourable.

@Pigster mentioned SF6. Evidently, S-F bonds are strong enough to compensate for the ionisation of S to S(VI), allowing 6 bonds to form.

Formation of 6 bonds means 12 electrons in the valence shell of sulphur. This is where it becomes evident that the octet rule is simply a guideline (based on similar reasons to what I have explained here). It seems reasonable however that sulphur has 6 valence electrons, so it can pair them all up to form 6 covalent bonds. The bottom line is, an atom will form as many bonds as it can with its valence electrons, as long as the bonds are strong enough. Take another cursed example, IF7. Iodine has 7 valence electrons, and I-F bonds are strong enough to pair up all of those electrons and form an outrageous 7 bonds.

Hope this helped.


Edit: I didn't explain the dative bond part of your question.
Formation of a dative bond doesn't involve oxidising sulphur because both of the bonding electrons come from the other species anyway. We need a different explanation.

The formation of a dative bond requires empty orbitals on the atom you're donating the electrons to, and those orbitals must be low enough energy to be able to easily put electrons into. The use of the 3d subshell is a reasonable guess, but I'd guess the energy of the 3d subshell is too high to just shove electrons into. Because the energy is so high, doing so would result in a more unstable product than the starting materials, which means the process is energetically unfavoured. Sadly this means the valence electron count is limited to 12.

Sadly going into more detail/clarification requires a more complicated bonding theory known as molecular orbital theory, which you'll encounter if you take chemistry at a higher level.
(edited 1 year ago)

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