Sigma and Pi Bonds

Moderators: Chem_Mod, Chem_Admin

Jane Burgan 1C
Posts: 73
Joined: Fri Sep 28, 2018 12:15 am

Sigma and Pi Bonds

Postby Jane Burgan 1C » Sun Nov 18, 2018 8:59 am

Which type of bond is stronger - a sigma bond or a pi bond?
Also, the textbook had this little chart:
A single bond is a sigma-bond. A double bond is a sigma-bond plus one pi-bond. A triple bond is a sigma-bond plus two pi-bonds.
Can someone explain this?

904936893
Posts: 62
Joined: Fri Sep 28, 2018 12:29 am

Re: Sigma and Pi Bonds

Postby 904936893 » Sun Nov 18, 2018 9:35 am

The first bond that two atoms make is a sigma bond. If two atoms have a double bond (i.e O=O) then they will have one sigma bond and one pi bond. If two atoms have a triple bond, like Nitrogen with Nitrogen, then there will be one sigma bond, and two pi bonds. So if two atoms are bound by more than one covalent bond, the additional orbitals will overlap side-by-side to form pi bonds. As to which is stronger, they're both covalent bonds so I'm not sure if either one is stronger than the other. However, pi bonds restrict the rotation of the two atoms they bind, making them rigid. I would think that is important information to know.

Ariel Cheng 2I
Posts: 67
Joined: Fri Sep 28, 2018 12:29 am

Re: Sigma and Pi Bonds

Postby Ariel Cheng 2I » Sun Nov 18, 2018 9:50 am

A single bond will always be a sigma bond, a double bond will be a sigma bond and a pi bond, and a triple bond will be a sigma bond and two pi bonds. The first bond is able to overlap head-on which allows the bound atoms to rotate. However, the second and third bonds are forced to bond side by side or in a parallel manner which makes it rigid and unable to rotate. Therefore I think Pi bonds are weaker.

Dimitri Speron 1C
Posts: 60
Joined: Fri Sep 28, 2018 12:17 am
Been upvoted: 1 time

Re: Sigma and Pi Bonds

Postby Dimitri Speron 1C » Sun Nov 18, 2018 12:14 pm

Pi bonds are weaker because due to the parallel overlap, the total area of overlap is smaller. This can be derived from quantum mechanical representations of the bonding models.

Bingcui Guo
Posts: 30
Joined: Fri Sep 28, 2018 12:19 am

Re: Sigma and Pi Bonds

Postby Bingcui Guo » Tue Nov 20, 2018 10:31 am

A single bond is always sigma bond since only s to s or p to p. But for double bond, the px to px is fixed, and the py and py, pz and pz are parallel side by side and they can form a sigma bond and pi bind.

Brice McKeown 3D
Posts: 35
Joined: Fri Sep 28, 2018 12:25 am

Re: Sigma and Pi Bonds

Postby Brice McKeown 3D » Thu Nov 22, 2018 12:13 am

Another thing I found helpful is that because the pi bonds are weaker they are more reactive!


Return to “*Molecular Orbital Theory (Bond Order, Diamagnetism, Paramagnetism)”

Who is online

Users browsing this forum: No registered users and 2 guests