Sigma vs Pi Bonds

$sp, sp^{2}, sp^{3}, dsp^{3}, d^{2}sp^{3}$

Quinton Sprague 1A
Posts: 94
Joined: Wed Sep 30, 2020 9:35 pm

Sigma vs Pi Bonds

Bit confused on how these two differ regarding their position on the internuclear axis. Believe Dr. Lavelle said Sigma bonds occur on the axis while Pi bonds are around the axis. What does this really mean about the electron interaction between two atoms? For Pi bonds one electron is above the other?

Malakai Espinosa 3E
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Re: Sigma vs Pi Bonds

I believe for sigma bond, their axises are positioned end to end, allowing for rotation. For pi bonds, the axises are side by side, meaning that they cannot rotate.

Sydney Lam_2I
Posts: 90
Joined: Wed Sep 30, 2020 10:09 pm

Re: Sigma vs Pi Bonds

I think the only thing you really need to understand is that sigma bonds allow the atoms to rotate, but pi bonds keep the structure as it is.

Manseej Khatri 2B
Posts: 76
Joined: Wed Sep 30, 2020 9:42 pm

Re: Sigma vs Pi Bonds

Sigma bonds occur on the internuclear axis, meaning the axis created by the interaction between the nucleus of two bonded atoms. Pi bonds occur when the orbitals are next to each other, allowing for the electrons to pair up, and this is not necessarily done on the internuclear axis. Pi bonds make it so that there is essentially two areas that attach the atoms to each other rather than one, and this prevents the atom from rotating independent of the molecule.

Ayesha Aslam-Mir 3C
Posts: 112
Joined: Wed Sep 30, 2020 9:43 pm

Re: Sigma vs Pi Bonds

I found this image on Chem Libre texts that might be helpful in visualizing the different bonds visually:

Frankie Mele 3J
Posts: 93
Joined: Wed Sep 30, 2020 10:09 pm

Re: Sigma vs Pi Bonds

Another thing to note is sigma bonds don't have any nodal planes containing the internuclear axis, whereas pi bonds have nodal planes and electron densities on both sides of the axis.

Libby Dillon - 1A
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Re: Sigma vs Pi Bonds

Sigma bonds interact end to end and allow bound atoms to rotate. They have cylindrical symmetry around the internuclear axis. Pi bonds overlap side by side and do not allow bound atoms to rotate without breaking bonds. Pi bonds result in electron density above and below the internuclear axis.

Emmeline Phu 1G
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Re: Sigma vs Pi Bonds

Hi! Sigma bonds involve two orbitals which interact end to end with each other; whereas a pi bond also involves two orbitals but instead of interacting end to end, they overlap side to side. Thus, the orbitals in a pi bond cannot be rotated or else the pi bond will break; however, sigma bonds allow bound atoms to rotate. Hope this helps! :)

Elizabeth Kaplan 3I
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Joined: Wed Sep 30, 2020 9:32 pm

Re: Sigma vs Pi Bonds

Sigma bonds allow bound atoms to rotate, thus the resulting sigma bond has electron density with cylindrical symmetry around the internuclear axis. On the other hand, pi bonds are between 2 orbitals, each with one electron, which are overlapped side by side, and thus the 2 regions of electron density are above and below, not along the internuclear axis.

FionaHunter21
Posts: 91
Joined: Wed Sep 30, 2020 9:37 pm

Re: Sigma vs Pi Bonds

How do we tell which way the internuclear axis is lined up?

Sydney Jensen 3L
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Re: Sigma vs Pi Bonds

A very important note is that the pi bonds cannot rotate due to their orbitals, but the sigma bonds are able to rotate.