[sam12103]

11. What is the hybridization of the carbon atom in the phosgene, Cl2CO? Give a complete description of the sigma and pie bonding in this molecule.

The answer in the back says

For the molecule COCl2: Hybridization of C=sp^2
Bonding:
 1 sigma bond between each chlorine and carbon (sp hybrid orbitals)
1 sigma bond between carbon and oxygen (sp hybrid orbitals)
1 pi bond between carbon and oxygen (p orbital)


I know how the book got the sigma bonds and pi bonds for the answer, but what I don’t understand is how to find out whether or not the sigma or pi bond is a sp hybrid orbital or a p orbital, which is indicated in the parentheses.

Can you please explain to me how to recognize and be able to label what is a sp and p?

Thank you

[Schrödinger]

I think the ones in the first 2 brackets are sp² hybrid orbitals and not sp hybrid orbitals.
I mean, the carbon is sp² hybridised. Where did sp hybrid orbitals come from?

The p-orbital part is ok.
Please check these and reply if you don't understand.

[BetaAmyloid]

First off, we need to take a look at the molecule.



When we are talking about electrons compared to hybridization, everyone two electrons are equal to one in hybridization.

In the same sense, every two electrons is ONE sigma bond. Every four electrons is TWO sigma bonds and ONE pi bond.
ONE sigma bond is considered s hybridization and TWO sigma bonds and ONE pi bond is considered sp hybridization and so on. Hybridization counts ONLY sigma bonds.

1 sigma bond between each chlorine and carbon (sp hybrid orbitals)

There is ONE sigma bond between EACH (there are TWO - so take that into account) chlorine and carbon. This means there are TWO sigma bonds overall. Every two electrons is one sigma bond. We have four electrons = two sigma bonds. Two sigma bonds means we have sp hybridization. Since, two electrons (one sigma bond) = s; four electrons (two sigma bonds) = sp; six electrons (three sigma bonds) = sp²; and so on.

1 sigma bond between carbon and oxygen (sp hybrid orbitals)

There is one carbon-oxygen bond. There are two sigma bonds here and one pi bond. AGAIN, We have four electrons = two sigma bonds. Two sigma bonds means we have sp hybridization. Since, two electrons (one sigma bond) = s; four electrons (two sigma bonds) = sp; six electrons (three sigma bonds) = sp²; and so on.

1 pi bond between carbon and oxygen (p orbital)

There is one carbon-oxygen bond. There are two sigma bonds here and one pi bond. This time though, they only want to count the PI BOND. One pi bond = p orbital = p hybridization.

DO NOT LISTEN TO SHRODINGER, HE IS WRONG.

Hope this helps.

[SigmaBond]

Don't listen to Shrodinger...he is wrong.

Cancer Curer is right...good job.

+1 snack

[Borek]

I think the ones in the first 2 brackets are sp² hybrid orbitals and not sp hybrid orbitals.
I mean, the carbon is sp² hybridised. Where did sp hybrid orbitals come from?

I believe what they mean by sp orbitals is not sp orbital as a final effect of hybridization, but rather way of signalling that orbital involved in bonding is one of those coming from sp^x hybrydization. There are three oribtals able to make sigma bonds in sp² hybridized carbon - and they refer to them as to sp orbitals, as opposed to s or p. But I see where the confusion comes from.

I would not state so easily you are wrong...

[Borek]

When we are talking about electrons compared to hybridization, everyone two electrons are equal to one in hybridization.

Please elaborate, I have troubles understanding what you mean.

Every four electrons is TWO sigma bonds and ONE pi bond.

The same. Four electrons are not creating three bonds.

[Schrödinger]

I think the ones in the first 2 brackets are sp² hybrid orbitals and not sp hybrid orbitals.
I mean, the carbon is sp² hybridised. Where did sp hybrid orbitals come from?

I believe what they mean by sp orbitals is not sp orbital as a final effect of hybridization, but rather way of signalling that orbital involved in bonding is one of those coming from sp^x hybrydization. There are three oribtals able to make sigma bonds in sp² hybridized carbon - and they refer to them as to sp orbitals, as opposed to s or p. But I see where the confusion comes from.


I would not state so easily you are wrong...

Please don't mistake my tone....

I think I'm pretty sure i am right and Cancer Curer made a mess with his explanation.

You do not hybridise C-Cl bonds and C-O bonds separately. Carbon's orbitals are hybridised only once, at the time of bond formation.

We have only 3 sigma bonds totally. Two C-Cl and one C-O, and one pi bond between C and O. Carbon uses 3 sp² orbitals for bonding with all atoms, as hybrid orbitals are used only for sigma bonding. And the one p-orbital that is free on the Carbon is used for pi-bonding.

Am I right?

[Borek]

You do not hybridise C-Cl bonds and C-O bonds separately. Carbon's orbitals are hybridised only once, at the time of bond formation.

We have only 3 sigma bonds totally. Two C-Cl and one C-O, and one pi bond between C and O. Carbon uses 3 sp² orbitals for bonding with all atoms, as hybrid orbitals are used only for sigma bonding. And the one p-orbital that is free on the Carbon is used for pi-bonding.

That's exactly how I see it - just remember what I wrote about probable meaning of the "sp" in the books answer, I believe they meant exactly the same.

[Schrödinger]

Thanks. I thought I was wrong and i was scared i had got the basics wrong. Thanks for the reassuring post.

[cth]

Yes, the "Cancer Curer"'s explanation is a mess and full of nonsense.  Obviously, he has limited understanding of what he is writing. A shame.

[...]
In the same sense, every two electrons is ONE sigma bond. Every four electrons is TWO sigma bonds and ONE pi bond.
[...]

1 sigma bond between carbon and oxygen (sp hybrid orbitals)

There is one carbon-oxygen bond. There are two sigma bonds here and one pi bond.
[...]

1 pi bond between carbon and oxygen (p orbital)

There is one carbon-oxygen bond. There are two sigma bonds here and one pi bond.
[...]

You must be kidding me    !!!! Are you talking of 3 bonds formed by 4 electrons? This case is extremely rare http://en.wikipedia.org/wiki/Three-center_four-electron_bond, and for COCl₂, it is certainly not the case.
I have the feeling that you don't realise that a double bond (like the C=O of the example) is made of one sigma bond (along the bond axis) and one pi bond (on the side of the axis) only.

You do not hybridise C-Cl bonds and C-O bonds separately. Carbon's orbitals are hybridised only once, at the time of bond formation.

We have only 3 sigma bonds totally. Two C-Cl and one C-O, and one pi bond between C and O. Carbon uses 3 sp² orbitals for bonding with all atoms, as hybrid orbitals are used only for sigma bonding. And the one p-orbital that is free on the Carbon is used for pi-bonding.

I agree with Schrödinger.



Let's explain hybridisation again:
* An isolated carbon atom possesses four atomic orbitals: 2s, 2p_x, 2p_y and 2p_z. The 2s is spherical and the 2p have two lobes pointing towards one direction: x, y and z. So, the angles between the 2p orbitals are 90º.
* However, when that carbon atom is place inside a molecule, the angles observed are never 90º. They are closer to: 109.5º, 120º and 180º. In order to explain this difference of angles between the expected 90º and the observed angles, the theory of hybridisation was proposed. It consists in mixing 2s and 2p orbitals together at the beginning to form new sp, sp² or sp³ orbitals (depending on the case). Then, the angles expected and observed agree (180º for sp, 120º for sp² and 109.5º for sp³).

The name sp means that the orbital 2s and only one orbital 2p mixed to form two hybridised sp orbitals. As a consequence, two 2p orbitals are left unhybridised and available to make two pi bonds.
The name sp² means that the one orbital 2s and two orbitals 2p mixed to form three hybridised sp² orbitals. As a consequence, there is one 2p orbital left unhybridised and available to make one pi bond.

Let's go to the example COCl₂:
* The carbon atom is hybridised sp². It has three orbitals sp² and one orbital 2p_z. It form three sigma bonds with the two Cl and O atoms, using the sp² orbitals. The 2p_z orbital make one pi bond with the oxygen atom.
* The oxygen atom is also hybridised sp². It has three orbitals sp² and one orbital 2p_z. The sp² orbitals form one sigma bond with the carbon and contain two lone pairs. The 2p_z orbital make one pi bond with the 2p_z from the carbon.
* The chlorine atoms are hybridised sp³: it has four orbitals sp³. They are used to make one sigma bond with the carbon and contain three lone pairs.

I know how the book got the sigma bonds and pi bonds for the answer, but what I don’t understand is how to find out whether or not the sigma or pi bond is a sp hybrid orbital or a p orbital, which is indicated in the parentheses.

Can you please explain to me how to recognize and be able to label what is a sp and p?

A pi bond always comes from two p orbitals of two adjacent atoms. It can't arise from one s orbital, it is impossible by symmetry.
Look at that short video of C₂H₄: http://www.youtube.com/watch?v=C2W-yDPcpl4
* In blue colour, you see the pi bond between the two carbon atoms. Notice how it is on the side of the C=C bond, and not directly in between the two C atoms.
* In green colour, you have the carbon sp² orbitals that form sigma bonds between the C and H atoms. See how the sigma bonds are directly in between the two atoms they are binding.
* In purple, you have the hydrogen 1s orbitals.

[cth]

Sorry, Cancer Curer, if yesterday I was hard on you in my previous post.

You can make mistakes, someone else will correct them. It's the way to learn and it's OK.
However, when you wrote:

DO NOT LISTEN TO SHRODINGER, HE IS WRONG.

I personally find it unacceptable to dismiss other people like that in order to impose your point of view, no matter how right or wrong it may be. And so, I replied in kind.