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Author Topic: In chemical bonding, what are sigma and pi bonds?  (Read 18817 times)

Offline farqueue

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Hi guys, i am doing an organic chemistry course this year and i am having trouble understanding....[xx(]

sp3, sp2 and sp bonds.
What are sigma and pi bonds?

appreciated if someone explained it in simple english, not textbook way. :D
« Last Edit: 22/11/2008 07:33:07 by chris »


 

Offline cuso4

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Re: In chemical bonding, what are sigma and pi bonds?
« Reply #1 on: 27/02/2006 19:10:57 »
The answer to your question all depends on how deep you want to go into this subject. Are you in University?

Think of sp3, sp2 and sp as hybrid of s and p orbitals.
For example in methane (CH4) the orbitals of the carbon atom is sp3 hybridised (one s + three p), this forms 4 equivalent orbital for hydrogen to bond to. and these orbitals get away as far as possible from each other to form a tetrahedral shape.

Can think about the other two hybridisation in the same way.
sp2 (one s + two p) - trigonal planar in shape. eg formaldehyde HCHO.
sp (one s + one p) - linear in shape. eg acetylene (=ethyne)

sigma bond = single bond (originate from overlap of s orbitals(H-H) or end-on overlap of p orbitals (C-C)
pi bond = double bond (originate from side-way overlap of p orbitals)

I hope the above is not too text-book like. It will be helpful to look at diagrams on books.

Angel
 

Offline cuso4

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Re: In chemical bonding, what are sigma and pi bonds?
« Reply #2 on: 27/02/2006 19:14:49 »
As you learn more about bonding models, you will find the above is not entirely correct. At the moment Molecular Orbital Theory is the best model for explaining bonding in molecules.

Angel
 

Offline farqueue

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Re: In chemical bonding, what are sigma and pi bonds?
« Reply #3 on: 01/03/2006 09:47:44 »
Thank you very much for your explanation. Yup, i am in university.

By the way, would u know why there is a decreasing trend in bond length as the no. of bonds increases?

For example:
Ethane has a bond length of 154pm
Ethene, 135
Ethyne, 120

Thanks in advance again
 

Offline anthony

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Re: In chemical bonding, what are sigma and pi bonds?
« Reply #4 on: 08/03/2006 08:38:42 »
The bond length goes down as the total bond strength goes up. An increased bonding between the atoms means the electron density between the two has increased. Therefore the positive nuclei repel each other less and come closer.
 

Offline DrDick

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Re: In chemical bonding, what are sigma and pi bonds?
« Reply #5 on: 31/03/2006 17:24:31 »
It helps if you think of a bond as existing because of the attraction of opposite charges.  Atomic nuclei are positively charged, while electrons are negatively charged.  Like charges repel, while opposite charges attract each other.  A bond occurs when the electrons are shared between two atoms.  The negatively charged electrons attract the positively charged nuclei.  More bonds imply more electrons between the atoms, which result in stronger attraction, bringing the atoms closer together.

DrDick
 

Offline Vadermort

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Re: In chemical bonding, what are sigma and pi bonds?
« Reply #6 on: 04/04/2006 14:41:23 »
Im doing the IB diploma...You know that sp hybridised molecules gives a linear shape right? and that sp2 gives a trigonal planar and sp3 gives a tetrahedral or trigonal pyramidal shapes. The eectrons form the delocalised pi bonds (double bonds) suround the entire area of the sigma (single) bond....
Geez...this is like a test.

b.s
 

Offline Chemistry4me

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Re: In chemical bonding, what are sigma and pi bonds?
« Reply #7 on: 22/11/2008 05:02:14 »
Can anybody tell me what type of hybridisation is a =c= (two double carbon bonds)? Its got two sigma and two pi bonds.. if my memory still serves me correctly...
 

Offline lightarrow

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In chemical bonding, what are sigma and pi bonds?
« Reply #8 on: 22/11/2008 12:55:07 »
Can anybody tell me what type of hybridisation is a =c= (two double carbon bonds)? Its got two sigma and two pi bonds.. if my memory still serves me correctly...
Where have you seen something like that?
 

Offline Chemistry4me

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In chemical bonding, what are sigma and pi bonds?
« Reply #9 on: 22/11/2008 22:30:20 »
Carbon suboxide, or tricarbon dioxide, C3O2, has four cumulative double bonds, making it a cumulene. It is closely related to CO, CO2 and C2O, and other oxides of carbon.

 

Offline Chemistry4me

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In chemical bonding, what are sigma and pi bonds?
« Reply #10 on: 23/11/2008 02:14:08 »
I found that stuff on Wikipedia, as soon as I saw this tricarbon dioxide I was facinated by its structure. Its very interesting, some molecules just defies the laws of chemistry.
 

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In chemical bonding, what are sigma and pi bonds?
« Reply #10 on: 23/11/2008 02:14:08 »

 

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