Covalent Bonding: O2 vs S8 - Understand the Logic

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Discussion Overview

The discussion revolves around the differences in bonding between O2 and S8, specifically exploring why sulfur forms S8 instead of S2. Participants examine the underlying logic and energy considerations in covalent bonding, touching on concepts from chemistry and quantum chemistry.

Discussion Character

  • Exploratory
  • Debate/contested
  • Technical explanation

Main Points Raised

  • Damian notes that O2 shares two pairs of electrons to achieve a stable electron configuration, questioning why sulfur forms S8 instead of S2.
  • One participant suggests that S8 has the lowest energy under certain conditions, indicating that there may not be a straightforward explanation for its formation.
  • Another participant expresses frustration with chemistry due to its numerous exceptions compared to physics, implying a perceived lack of systematic rules.
  • A different viewpoint suggests that if the rule is that the system with the lowest energy is observed in nature, then exceptions may not be valid, but this complicates simple explanations like the "stable octet."
  • One participant argues that the many exceptions in chemistry may indicate that the true conditions of the rules are not yet fully understood.
  • A later reply introduces quantum chemistry concepts, explaining that electron correlation affects bonding in O2 and S8 differently, with sulfur's larger orbitals leading to simpler bonding scenarios.
  • It is noted that the energetic differences between various sulfur allotropes (S4, S6, S8) are minor, complicating predictions about stability.

Areas of Agreement / Disagreement

Participants express a range of views, with some agreeing on the complexity of bonding rules in chemistry while others highlight the lack of consensus on the underlying principles governing sulfur's bonding behavior. The discussion remains unresolved regarding the clarity and completeness of the rules in chemistry.

Contextual Notes

Participants acknowledge limitations in the explanations provided, particularly regarding the oversimplification of rules and the complexities introduced by real systems versus idealized models.

dnorric
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Ok I understand that O2 wants to have a stable number of electrons for its period which is 8 and so it shares two pairs of electrons. But what about S8. I thought it would form S2. Why is it forming S8, what is the logic.
Cheers
Damian
 
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I am afraid there is no simple logic behind. For some reasons S8 has the lowest energy in a given circumstances. Quite often that's just the way it is and it is not possible to give a systematic explanation other than "if you calculate the energy of different molecules, there is a minimum here".
 
This is why chemistry drives me crazy. There are so many exceptions to the rule, it hardly seems a science in comparison to physics. Thanks heaps for your help though

Borek said:
I am afraid there is no simple logic behind. For some reasons S8 has the lowest energy in a given circumstances. Quite often that's just the way it is and it is not possible to give a systematic explanation other than "if you calculate the energy of different molecules, there is a minimum here".
 
dnorric said:
This is why chemistry drives me crazy. There are so many exceptions to the rule, it hardly seems a science in comparison to physics. Thanks heaps for your help though

That's what happens when you study real systems instead of idealized models :p
 
dnorric said:
There are so many exceptions to the rule, it hardly seems a science in comparison to physics.

It depends on the selection of the rule. If the rule is "whichever system has the lowest energy, is the one observed in nature", this is not an exception.

But then you can't explain the system in the simple terms like "stable octet"...

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I think Mathematics and Physics are the ultimate weapons in dealing with Chemistry...
 
Since there are so many exceptions to the rule, perhaps it's just that we have yet to find the true and complete conditions of the rule. Just a thought...
 
There are many exceptions because the rule is oversimplified.

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There is a logic. Take some classes in quantum chemistry.
In the case of oxigen and sulfur the problem has to do with electron correlation.
Loosely speaking, in Oxigen the electrons are already so densely packed, that O2 tries to avoid contact with other oxigen atoms or molecules and instead develops a very strange double bond. In sulfur the orbitals are so much larger that electronic correlation is not a relevant topic any more. So it forms rather simplistic single bonds. The energetic differences between S4 S6 S8 to S_infinity are rather minute so that it is quite difficult to predict which one is actually most stable.
 

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