Chad's Prep There was a “trick” question on the exam I took yesterday that had to do with just this concept. I wouldn’t have gotten it right if it weren’t for you. Thanks!!
I have a question about the Lewis structure for SO3 sulfur trioxide. One of the other channels that I watch drew it with three double bonds and he said that is best because you get the lowest formal charge possible. That seemed fine to me but in the comments there was an angry commenter saying that actually you should put a double bond for just one of the oxygen atoms, analogous to nitrate and carbonate (with three resonance structures, meaning that you get 1.33 for the bond order). His rational was that the sulfur is sp2 hybridized so you only have one p orbital to work with, and he said that if you had double bonds on more than one of the oxygens there would be unreasonable orbital overlap. Once I read that I figured that was correct, but I wanted to verify with another source. Wikipedia shows all the possible resonance structures. They show it with three double bonds, with two double bonds, and with one double bonds. Well, according to the angry commenter, you should not include the resonance structures with two or three double bonds because of unreasonable orbital overlap, so Wikipedia and the angry commenter seem to be at odds. So next I googled bond order of sulfur trioxide. There are definitely some places on the web saying it is indeed 1.33, which suggests that the angry commenter is right, but I'm not finding consistent and authoritative information. Thank you for your help.
Great question science nerd! The issue you're running into is a result of the shortcomings of Lewis structures and the use of hybrid orbitals in Valence Bond Theory to give an accurate description of the bonding occurring in SO3 (which is an issue you'll more commonly run into for atoms with expanded octets). This might blow your mind but hybrid orbitals don't actually exist! But the use of hybrid orbitals in Valence Bond Theory does accurately predict the correct bond angles in most molecules and therefore has its utility, but the truth is actually more complicated and is better described by Molecular Orbital Theory (I cover this in brief in lesson 9.5, but I only cover diatomics; polyatomics like SO3 are even more complicated). I did a brief search and couldn't find a great picture of the molecular orbitals for SO3, but you can find them pretty readily for H2O or CH4 to see examples, though neither of these involve pi bonding. Back to SO3, both the structure with 3 double bonds and the set of resonance structures are commonly accepted Lewis Structures for SO3. Many would say that the best structure has the lowest formal charges and would go with 3 double bonds. To avoid confusion test questions are sometimes worded "Draw the Lewis structure for SO3 for which all atoms obey the octet rule." In this case then you'd be going with the set of resonance structures. Now the commenter you cite went with the resonance structures because it was consistent with the idea that the sulfur is sp2 hybridized and therefore wouldn't have sufficient unhybridized p orbitals to make 3 pi bonds. But if we realize that hybrid orbitals don't even exist then we don't have to cling to these as the best structures. I would be content to say that neither is a perfect description of reality but if I had to pick a better structure (one that is more consistent with reality) I would tend to go with the three double bonds. I base this on bond lengths. Having a bond order of 2 vs a bond order of 1.33 is a substantial difference and would be reflected in the bond strength and length. A bond order of 2 would reflect a stronger and shorter bond. If we first take a look at the Lewis structure for dimethylsulfoxide you'll see that it is pretty universally accepted that it has a sulfur-oxygen double bond, and it's bond length is reported as right around 149pm. The sulfur-oxygen bond lengths in SO3 are reported as being even a little shorter at 142pm. So if I had to pick a bond order of either 1.33 or 2, I'd definitely go with 2. And you see something similar in SO2. You'll find a very similar debate for the Lewis structure for SO2 (is there a double bond to both oxygen atoms--a bond order of 2; or are there two resonance structures with 1 single and 1 double bond--a bond order of 1.5). But the S-O bond length in SO2 is reported as 143pm, which therefore also looks more consistent with a bond order of 2. In cases like this I think it best not to get too dogmatic. No need to argue too much about which structure is right in a model that in this particular case is falling short in providing an accurate picture of reality. Hope this helps!😜
Your explanation of resonance at 35:00 is amazing. Thank you for all that you do.
Glad you found it helpful Anthony! And you are very welcome!
Chad's Prep There was a “trick” question on the exam I took yesterday that had to do with just this concept. I wouldn’t have gotten it right if it weren’t for you. Thanks!!
@@anthonysorendino You are welcome, Anthony - glad to hear the videos paid off for you!
We gotta get him that tesla. I'm watching every ad and liking every video. LOL.
Thanks Keng! No ads as of yet but I really appreciate the likes! Happy Studying!
yes! we all need to. Especially those of us taking the DAT. @Chad's Prep, is there a reason you have no ads? I would gladly watch them all
how did you do on the DAT@@ajike
I love his way of teaching
Thank you for saying so, Rana.
Great explanation!
Glad it was helpful, Arthur - thanks for your comment!
Thank you so much !!
You're welcome, Katelynn!
You are a legend! thanks
You're welcome - thank you!
I have a question about the Lewis structure for SO3 sulfur trioxide. One of the other channels that I watch drew it with three double bonds and he said that is best because you get the lowest formal charge possible. That seemed fine to me but in the comments there was an angry commenter saying that actually you should put a double bond for just one of the oxygen atoms, analogous to nitrate and carbonate (with three resonance structures, meaning that you get 1.33 for the bond order). His rational was that the sulfur is sp2 hybridized so you only have one p orbital to work with, and he said that if you had double bonds on more than one of the oxygens there would be unreasonable orbital overlap. Once I read that I figured that was correct, but I wanted to verify with another source. Wikipedia shows all the possible resonance structures. They show it with three double bonds, with two double bonds, and with one double bonds. Well, according to the angry commenter, you should not include the resonance structures with two or three double bonds because of unreasonable orbital overlap, so Wikipedia and the angry commenter seem to be at odds. So next I googled bond order of sulfur trioxide. There are definitely some places on the web saying it is indeed 1.33, which suggests that the angry commenter is right, but I'm not finding consistent and authoritative information. Thank you for your help.
Great question science nerd! The issue you're running into is a result of the shortcomings of Lewis structures and the use of hybrid orbitals in Valence Bond Theory to give an accurate description of the bonding occurring in SO3 (which is an issue you'll more commonly run into for atoms with expanded octets). This might blow your mind but hybrid orbitals don't actually exist! But the use of hybrid orbitals in Valence Bond Theory does accurately predict the correct bond angles in most molecules and therefore has its utility, but the truth is actually more complicated and is better described by Molecular Orbital Theory (I cover this in brief in lesson 9.5, but I only cover diatomics; polyatomics like SO3 are even more complicated). I did a brief search and couldn't find a great picture of the molecular orbitals for SO3, but you can find them pretty readily for H2O or CH4 to see examples, though neither of these involve pi bonding.
Back to SO3, both the structure with 3 double bonds and the set of resonance structures are commonly accepted Lewis Structures for SO3. Many would say that the best structure has the lowest formal charges and would go with 3 double bonds. To avoid confusion test questions are sometimes worded "Draw the Lewis structure for SO3 for which all atoms obey the octet rule." In this case then you'd be going with the set of resonance structures.
Now the commenter you cite went with the resonance structures because it was consistent with the idea that the sulfur is sp2 hybridized and therefore wouldn't have sufficient unhybridized p orbitals to make 3 pi bonds. But if we realize that hybrid orbitals don't even exist then we don't have to cling to these as the best structures.
I would be content to say that neither is a perfect description of reality but if I had to pick a better structure (one that is more consistent with reality) I would tend to go with the three double bonds. I base this on bond lengths. Having a bond order of 2 vs a bond order of 1.33 is a substantial difference and would be reflected in the bond strength and length. A bond order of 2 would reflect a stronger and shorter bond.
If we first take a look at the Lewis structure for dimethylsulfoxide you'll see that it is pretty universally accepted that it has a sulfur-oxygen double bond, and it's bond length is reported as right around 149pm. The sulfur-oxygen bond lengths in SO3 are reported as being even a little shorter at 142pm. So if I had to pick a bond order of either 1.33 or 2, I'd definitely go with 2.
And you see something similar in SO2. You'll find a very similar debate for the Lewis structure for SO2 (is there a double bond to both oxygen atoms--a bond order of 2; or are there two resonance structures with 1 single and 1 double bond--a bond order of 1.5). But the S-O bond length in SO2 is reported as 143pm, which therefore also looks more consistent with a bond order of 2.
In cases like this I think it best not to get too dogmatic. No need to argue too much about which structure is right in a model that in this particular case is falling short in providing an accurate picture of reality.
Hope this helps!😜
i love you mr clean
Excellent - I beam with pride!