formal charge?

[laya533]

does anyone know what is the formal charge on the central atom of POCl3?
thanks

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[TicAL]

+1

 

[izibo]

um... or zero.

 

[laya533]

which one?

 

[QofQuimica]

It depends on which resonance form you draw. One looks like this:

O=P(Cl)3 and that one would have formal charge of 0.

The other looks like this:

-O-P+(Cl)3 and that would give P a formal charge of +1.

I'd go with the 0 because they probably would draw the first one.

 

[TicAL]

O=P(Cl)3 isn't a resonance structure...there's only one correct Lewis structure for this compound. When drawing Lewis structures you connect the atoms with the fewest amount of bonds as possible. Then you rearrange any double bonds if there are any. In this case there's only 4 bonds around the P...if you add a 5th bond it isn't a resonance strucuture.

 

[QofQuimica]

O=P(Cl)3 isn't a resonance structure...there's only one correct Lewis structure for this compound. When drawing Lewis structures you connect the atoms with the fewest amount of bonds as possible. Then you rearrange any double bonds if there are any. In this case there's only 4 bonds around the P...if you add a 5th bond it isn't a resonance strucuture.

Yes, it is. There are multiple correct Lewis structures for compounds that have more than one distinct resonance contributors like this one does. Remember that resonance structures have the same atom connectivities; only the electrons have moved. In this case, I am moving the third lone pair from the oxygen and making a new bond to phosphorus to form the double bond. I am not moving any atoms; thus, it is a resonance structure and not a structural isomer. If there were a nitrogen in the center instead of the phosphorus, the double bond resonance structure would not be possible, since N cannot exceed its octet. However, P is a third row element, so it CAN have five bonds; sometimes it even takes on a trigonal bipyramidal molecular geometry if all five bonds are single bonds.

 

[TicAL]

The definition of a resonance structure has to do with maintaining the same amount of both lone pairs and bond pairs in a Lewis structure. Valid resonance structures of a compound always have the same number of lone pairs and bond pairs...but in different instances can be rearranged.

 

[QofQuimica]

The definition of a resonance structure has to do with maintaining the same amount of both lone pairs and bond pairs in a Lewis structure. Valid resonance structures of a compound always have the same number of lone pairs and bond pairs...but in different instances can be rearranged.

Not necessarily. Resonance structures do have to have the same connectivity and the same total number of electrons, but they do NOT have to have the same numbers of bonding versus nonbonding pairs in each of two distinct resonance contributors. For example, you can draw a resonance structure of a carbonyl compound that has an extra lone pair on O that comes from the double bond between C and O: -O-C+(R)2 versus the more common O=C(R)2 representation. This is analogous to the situation of the compound that we are talking about here. An even better example in this context is an ylide, which can either be represented as -C-P+(R)3 or C=P(R)3.

 

[izibo]

See, this is what I hate about pre-meds... everyone thinks they are right and refuses to think through ANYTHING.

Phosphorus is one of those nifty atoms that is capable of having an expanded octet. It can have 10 or even 12 electrons floating around it. For instance, look at Phosphate, that has 10 electrons floating around the central phosphorus: three single bonded oxygens and a double bonded oxygen.

POCl3 is not a resonance stablized molecule. The oxygen is double bonded to the phosphorus and the three chlorines are have a single bond each. It has an expanded octet.

The image shown at the following website is correct.

http://www.chem.ox.ac.uk/inorganicchemistry3/P/POCl3.html

So, in conclusion, the one and only formal charge is 0

 

[izibo]

Oh, and if people don't believe me about POCl3 NOT being resonance stabled, you can visit this site

http://www.colby.edu/chemistry/webmo/POCl3.html

which has a significant amount of data on POCl3 included the % of the time it is in which form and the bond lengths and angles.

 

[tigress]

See, this is what I hate about pre-meds... everyone thinks they are right and refuses to think through ANYTHING.

Phosphorus is one of those nifty atoms that is capable of having an expanded octet. It can have 10 or even 12 electrons floating around it. For instance, look at Phosphate, that has 10 electrons floating around the central phosphorus: three single bonded oxygens and a double bonded oxygen.

POCl3 is not a resonance stablized molecule. The oxygen is double bonded to the phosphorus and the three chlorines are have a single bond each. It has an expanded octet.

The image shown at the following website is correct.

http://www.chem.ox.ac.uk/inorganicchemistry3/P/POCl3.html

So, in conclusion, the one and only formal charge is 0

You know, QofQuimica almost has her PhD in I forget what but it has to do with chemistry. She knows what she's talking about. Besides, that second website you link to doesn't talk about resonance stabilization, but it mentions the delocalization of the electrons, which is what resonance structures depict anyway.

 

[izibo]

Good for her... and if you look at the measurements on the website you can infer that it is not resosnance stabilized based on bond lengths. For instance, the double bond would be longer if it was resonance stabilized.

But, again... I really do not care if I convince you or not. If you want to think the formal charge is +14 be my guest

 

[tigress]

Good for her... and if you look at the measurements on the website you can infer that it is not resosnance stabilized based on bond lengths. For instance, the double bond would be longer if it was resonance stabilized.

But, again... I really do not care if I convince you or not. If you want to think the formal charge is +14 be my guest

I was just responding to your "See, this is what I hate about pre-meds... everyone thinks they are right and refuses to think through ANYTHING." It seemed very condescending. I hardly know anything about chemistry so I'm certainly not one to argue with you.

 

[QofQuimica]

Oh, and if people don't believe me about POCl3 NOT being resonance stabled, you can visit this site

http://www.colby.edu/chemistry/webmo/POCl3.html

which has a significant amount of data on POCl3 included the % of the time it is in which form and the bond lengths and angles.

lmfao, izibo, you don't have to take my word for there being more than one resonance structure on the grounds that I'm getting my PhD; YOUR link provides ample proof that I'm right. One, check out the P=O bond order: it's 1.735, not 2.000. That means that it DOES have some single bond character, as I have been arguing all along. The closest thing I saw for a P-O single bond was for (HO)3P on that same site which has a length of 1.678 ang, versus 1.467 ang for the (very nearly) double bonds of O=P=O; our compound's P-O bond comes in nicely between the two extremes at 1.487 ang. But my personal favorite part from your link is the following (emphasis mine):

"The Lewis structure that is closest to your structure is determined. The hybridization of the atoms in this idealized Lewis structure is given in the table below. Please note that your structure can't be well described by a single Lewis structure, because of extensive delocalization."

What does that last sentence mean? It means that there is more than one resonance contributor needed to fully describe the molecule's structure.

 

[Shrike]

See, this is what I hate about pre-meds... everyone thinks they are right and refuses to think through ANYTHING.

I readily admit that I do not know chemistry: I last took a class in it before you were born, I suspect. But even I can tell from the web page whose address you provided that it refutes your position. That, plus Q's obvious expertise in the subject (OK, obvious to those of us who have encounterd her before; apparently not so obvious to some of the newer forum participants), suggests to me that you should consider the irony of your own words.

I wouldn't have looked at a chemistry thread, but a friend told me I would think this one amusing. That turned out to be right.

 

[researchprof]

QofQuimica is right. O=P(Cl)3 does have -O-P+(Cl)3 as a resonant structure. Just know that pi electrons can be delocalized. There is a delocalizable pi electron pair in O=P bond; and oxygen is more electronegative than P, so it would bear a charge of -1 in the resonant form.

 

[sushi320]

Well you all seem to be praising QofQuimica, and although I don't argue her knowledge on this matter. I understand the guy's frustration and why he was being condescending to her. And I don't think I disagree with him.

Before you flame me, look at the original poster's question. The guy wanted to know the formal charge as it applies to a question, the very question that i also needed help on, which made me google it, and this thread came up. The correct answer, was a formal charge of zero.

But people like QofQuimica, find it their duty to spill her own insecurities for whatever reason, by providing correct, but needlessly trivial information, in an attempt to show her superiority (a consequence of insecure people). Although that structure has been known to have "resonance", it is not something you would need to know in that much detail. I mean, technically, orbitals for electrons are just estimations of where you would find them on the atom, there is no saying that that is always the path 100% of the time for the electron of a specific orbital, so can I dispute that the orbital information is wrong?

Just answer the damn question of the post. Nuff said.

 

[Timaeus]

Well you all seem to be praising QofQuimica, and although I don't argue her knowledge on this matter. I understand the guy's frustration and why he was being condescending to her. And I don't think I disagree with him.

Before you flame me, look at the original poster's question. The guy wanted to know the formal charge as it applies to a question, the very question that i also needed help on, which made me google it, and this thread came up. The correct answer, was a formal charge of zero.

But people like QofQuimica, find it their duty to spill her own insecurities for whatever reason, by providing correct, but needlessly trivial information, in an attempt to show her superiority (a consequence of insecure people). Although that structure has been known to have "resonance", it is not something you would need to know in that much detail. I mean, technically, orbitals for electrons are just estimations of where you would find them on the atom, there is no saying that that is always the path 100% of the time for the electron of a specific orbital, so can I dispute that the orbital information is wrong?

Just answer the damn question of the post. Nuff said.

Eh... this is a poor interpretation of what happened.

It went down like this.

OP asks a question.

Response 1 says: +1

Response 2 says : 0

These are conflicting answers, sort of. What does QofQuimica do?

She tries not to make anyone look silly by pointing out that it will depend on how you draw the Lewis structure. AND, in the end, notes that the O=P(Cl)_3 is the more representative Lewis structure, and suggests that the OP consider the formal charge 0.

In attempt to display superiority? Hardly.

It was only after one (or a few) inappropriately aggressive response did she have to defend her acceptable interpretation. By mentioning resonance structures, one poster misunderstood her and thought that she was suggesting the compound was resonance-stabilized, in the sense I suppose that we think of benzene to be resonance-stabilized - however, the compound the OP refers to is not (in that same sense).

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To everybody:


Don't forget to mention in your personal statements how passive aggressive AND compassionate you are!

 

[BloodySurgeon]

Eh... this is a poor interpretation of what happened.

It went down like this.

OP asks a question.

Response 1 says: +1

Response 2 says : 0

These are conflicting answers, sort of. What does QofQuimica do?

She tries not to make anyone look silly by pointing out that it will depend on how you draw the Lewis structure. AND, in the end, notes that the O=P(Cl)_3 is the more representative Lewis structure, and suggests that the OP consider the formal charge 0.

In attempt to display superiority? Hardly.

It was only after one (or a few) inappropriately aggressive response did she have to defend her acceptable interpretation. By mentioning resonance structures, one poster misunderstood her and thought that she was suggesting the compound was resonance-stabilized, in the sense I suppose that we think of benzene to be resonance-stabilized - however, the compound the OP refers to is not (in that same sense).

--
To everybody:


Don't forget to mention in your personal statements how passive aggressive AND compassionate you are!

Although we can argue all day about who said what, I would perfer to end the discussion with the fact the question has been answered and we may now continue with our studying.

Closing Thread.