Talk:Sulfur trioxide

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Contents 1 Bonding 2 Nomenclature 3 Cookbook for sulfur trioxide? 4 Sigma Aldrich 5 Crystal Structure 6 Structure of Solid 7 Reversion of H2SO4 to SO3 and Water 8 Stub

[edit] Bonding

What is the bond structure of SO₃?

Not a simple question! The physical fact is that SO₃ is trigonal planar with three equivalent sulfur–oxygen bonds. It is usual to describe these bond as double bonds, thus breaching the octet rule. For a more complete description of the theoretical controversy surrounding such breaches of the octet rule, see hypervalent molecule. I would add that IMHO sulfur–oxygen π-bonds have a relatively minor contribution to the overall bonding scheme. Physchim62 08:38, 24 May 2005 (UTC)

Erm... Actually, it's a very simple question. The octet rule only really applies to the 2nd period. Elements in period 3 or lower have access to the d-subshell (the transition metal block). As a result, they have a maximum of 18 outer shell electrons. Hence, for transition metals and lower main group chemistry, the 18 electron rule can be used instead.

So: Sulphur Trioxide... 3 Oxygen atoms which can only be at an oxidation state of -2 (because oxygen doesn't like anything other than -2 or 0), so subtract that leaves 12 outer shell electrons around the sulphur nucleus. Thus sulphur is present in it's +4 oxidation state. All oxidation states comply and the total of 18 electrons is maintained.

Oh, anf FYI, the molecule exhibits sp<sup3d hybridisation, unless I'm mistaken. I'm a little hazy on the exact bonding structure, however... It's been a couple of years. --Xanthine 12:14, 25 January 2006 (UTC)

I've never seen the 18 electron rule applied to main group compounds: it is widely breached for transition metal compounds in any case. And the sulfur in sulfur trioxide is in oxidation state +6... Physchim62 (talk) 14:03, 25 January 2006 (UTC)

@Xanthine: It's sp² hybridization, hence the trigonal planar shape. --Spoon! 08:01, 31 August 2006 (UTC)

[edit] Nomenclature

(Transferred from main article and edited for HTML. Physchim62 20:12, 16 September 2005 (UTC))

The nomenclature in the synthesis of SO₃ is not correct. Sodium bisulfate = sodium pyrosulfate = NaHSO₄. On the contrary, Sodium PERsulfate is something quite different: Na₂S₂O₈. This is probably what is synthesised. 131.174.15.229 10:09, 12 September 2005 (UTC)

• Sodium bisulphate is NaHSO₄, sodium pyrosulphate is Na₂S₂O₇. Historically, this has often been written Na₂SO₄.SO₃ particulally in patents. This does give off SO₃ when strongly heated.

• To make the Persulphate, a strong oxidising agent, you need another oxidising agent, typically hydrogen peroxide or by electrolysis, though this is not a good method to make sulphur trioxide. Ambix 20:24, 14 December 2005 (UTC)

[edit] Cookbook for sulfur trioxide?

What's up with the cookbook recipe-like section on how to make sulfur trioxide? It's pretty funny, the way it's written, to read, though. ;) Bayerischermann 23:53, 2 October 2005 (UTC)

[edit] Sigma Aldrich

The link "Sigma Aldrich" does not guide me to a specific page about "Sulfur trioxide". It seems, that this is a spam link.

More about "chemical suppliers": http://en.wikipedia.org/wiki/User_talk:213.188.227.119

Best regards

[edit] Crystal Structure

I believe that the gamma form is hexagonal, but I can't find a reference to verify this. Anybody who can verify this is invited to add the fact to the Crystal Structure paragraph. Karlhahn 17:37 13 August 2006 (UTC)

[edit] Structure of Solid

Smokefoot has eliminated the conditions under which the mixed alpha-beta-gamma forms arise. The section as it now stands begs the question of how to get the beta form. Karlhahn 19:15, 21 August 2006 (UTC)

I will be re-revising this rapidly changing but important article. I left a note on your Talk page. --Smokefoot 22:26, 21 August 2006 (UTC)

[edit] Reversion of H₂SO₄ to SO₃ and Water

The text currently contains the sentence, "Only upon heating to ~340 °C does sulfuric acid revert to sulfur trioxide and water." This suggests that you can separate H₂SO₄ into SO₃ and water simply by heating it. In reality you end up with a mixture of two gases (actually three gases because thermodynamics requires that some H₂SO₄ remain no matter how hot you get it) and like any gas mixture, it does not magically separate. So perhaps a qualifier to the sentence is in order -- something like, "although this is not a feasible means of separating H₂SO₄ into SO₃ and water." Karlhahn 01:25, 22 August 2006 (UTC)

Yeah, I wrote or re-re-revised the offending bit. You go ahead and edit away. You do it your way. The main problem is specifying the temperature, implying that magically the equilibrium jumps to 100% conversion. Nice catch. --Smokefoot 01:39, 22 August 2006 (UTC)

[edit] Stub

Is this page still classified as a stub --Dinna89 12:10, 15 August 2006 (UTC)

No, its long enough to be a "start", but still needs some cleanup. Physchim62 (talk) 17:06, 17 August 2006 (UTC)