Sigma & Pi Bonds

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Emily Vainberg 1D
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Joined: Sat Jul 20, 2019 12:15 am

Sigma & Pi Bonds

Postby Emily Vainberg 1D » Sat Nov 16, 2019 1:17 pm

Does anyone who has taken AP chem know how easy sigma & pi bonds are? He said he is going to go over it in class for a few minutes, but with the test so soon I wanted to know how difficult the concept is.

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Joined: Sat Aug 17, 2019 12:16 am

Re: Sigma & Pi Bonds

Postby lilymayek_1E » Sat Nov 16, 2019 1:30 pm

sigma and pi bonds are fairly easy to understand; the names are more used for identification more than anything else. sigma bonds are the first bonds that form between two atoms (that first line when you draw between two atoms in a diagram). pi bonds are any more bonds after that (double bond, triple...), where orbitals between two atoms overlap laterally. pi bonds strengthen and shorten the initial sigma bond, as well as lock electrons "in place" within a bond (Lavelle talked about this "locking" mechanism with cis & trans-dichloroethene in lecture).
I think the main thing to understand would just be sigma=first bond, pi=any bond after, helps strengthen&shorten!

Hannah Romano 4D
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Joined: Sat Aug 24, 2019 12:18 am

Re: Sigma & Pi Bonds

Postby Hannah Romano 4D » Sat Nov 16, 2019 2:46 pm

A sigma bond is the first bond between atoms. Pi bonds are the second or third bonds. In the example that was introduced in lecture, the sigma and pi bonds are relevant in biological molecules which have cis and trans isomers. This means that the molecules have the same molecular formula but a different structure where identical atoms are either on the same side of the molecule or opposite sides. Sigma and pi bonds are then relevant here because, when there is only a sigma bond (i.e. single bond) the atoms can rotate about the molecule so no cis or trans structure can exist as the carbon atoms will be constantly rotating and shifting the position of the bonded atoms. When a pi bond is added, atoms can no longer rotate allowing for cis and trans structures to form.

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Re: Sigma & Pi Bonds

Postby faithkim1L » Sat Nov 16, 2019 3:15 pm

Sigma bonds are the first bonds between any two atoms. So, for single bonds, there are only sigma bonds. However, for double and triple bonds, pi bonds are the other bonds (2nd and 3rd bonds) formed between two atoms. So for a double bond, there will be one sigma bond and one pi bond. The pi bonds are harder to break, which is one of the reasons why double and triple bonds are harder to break than single bonds.

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Re: Sigma & Pi Bonds

Postby 805291863 » Sat Nov 16, 2019 3:46 pm

Does anyone know what type of questions we will be asked regarding sigma and pi bonds? For example, will we just have to identify how many of each type is present in a bond? Will we have to be able to draw it?

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