## Bond Strengths

Phoebe Chen 4I
Posts: 55
Joined: Fri Sep 28, 2018 12:29 am

### Bond Strengths

In the 6th Edition textbook section 4.7 it says "a carbon-carbon double bond is stronger than one carbon-carbon single bond but weaker than the sum of two single bonds." I understand why a C-C double bond is stronger than a single bond but I am confused about it being stronger than the sum of two single bonds. Can someone please explain this to me?

The textbook also says "because the p-orbitals overlap in a side-by-side fashion, the overlap in a pi-bond is smaller and weaker than the end-to-end overlap that results in a sigma-bond." I thought it was the opposite where pi-bonds were stronger and because they overlapped side-by-side they actually overlapped more. Can someone please explain this to me too? I really appreciate it!

Amy Dinh 1A
Posts: 62
Joined: Fri Sep 28, 2018 12:23 am

### Re: Bond Strengths

In a Carbon Carbon double bond, it consists of one pi bond and one sigma bond. Pi bonds are weaker than sigma bonds due to less overlap between the p-orbitals, so therefore, the double bond (1 pi bond and 1 sigma bond) is less than the sum of 2 sigma bonds.
Hope this helps!

Carlos De La Torre 2L
Posts: 60
Joined: Tue Oct 09, 2018 12:16 am

### Re: Bond Strengths

a pi bond is weaker than a sigma bond because it is higher energy than a sigma bond, remember everything wants to be in the lowest energy state possible, pi bonds have a nodal plane between the nuclei which is where the electrons would like to be therefor it is weaker than a sigma bond as the electron concentration is by one nucleus as opposed to between two nuclei in a sigma bond

Posts: 64
Joined: Fri Sep 28, 2018 12:26 am

### Re: Bond Strengths

A C=C double bond is stronger than a single bond but it is weaker than the sum of 2 single C-C bonds. Sigma bonds are harder to break than pi bonds because sigma bonds have their overlap closer to both of the atom's nuclei and the electrons are more attracted to the nuclei because of the positive charge of the nucleus. Pi bonds are oriented in a side by side fashion which makes the electrons in these regions farther from the nucleus. The farther the electrons are from the nucleus then the easier it is to break the bond since the electrostatic forces are not as strong. This is why 2 C-C single bonds are stronger than 1 C=C double bond.

caseygilles 1E
Posts: 73
Joined: Fri Sep 28, 2018 12:18 am

### Re: Bond Strengths

The reason why a carbon carbon double bond is weaker than the sum of two carbon carbon single bonds is because a Sigma bond is much stronger than a pi bond, therefore two Sigma bonds are stronger than a Sigma bond plus a pi bond. This also has to do with rotation because Sigma bonds are allowed to rotate, which shows their ability to move makes them stronger. Since pi bonds are oriented vertically, they cannot rotate and so are easier to break than Sigma bonds