Pi and Sigma Bonds

[Shuyi Yu 1B]

Whats the difference between pi and sigma bonds? And why can there be two pi bonds but not two sigma bonds?

[Mindy Kim 4C]

The difference in pi and sigma bonds lies in how the orbitals in a bond are oriented. In a sigma bond, the orbitals of the atoms involved in the bond overlap end to end while in a pi bond, the orbitals overlap in two places side by side. Therefore, pi bonds cannot be rotated without breaking the bond. There can be two pi bonds in a triple bond (two pi and one sigma), however there can never be more than one sigma bond.

[Daniel_Frees_1L]

Also, I believe bonds always start with a sigma bond, and then pi bonds are added onto that with further bonding between the two atoms.

[Madeera_Mian_3B]

Also, Pi bonds are present with bonds greater than single bonds. Sigma bonds are present in single bonds and also double and triple bonds.

[A De Castro 14B 2H]

I've always thought of sigma bonds as "head on collisions" between two orbitals, while pi bonds are just sideways overlaps between two orbitals. Once orbitals have "collided," they can't collide anymore, i.e. once a sigma bond has been formed between two atoms/molecules, another sigma bond can't form.