Question

What is the difference between a sigma bond and a pi bond?

Answer 1

A bond has cylindrical symmetry; a bond has a nodal plane that includes the bond axis.

Sigma Bonds

A bond comes from the end-to-end overlap of the bonding orbitals. The common forms of sigma bonds are shown below.

Sigma bonds are cylindrically symmetrical. This means that if you draw a line along the internuclear axis, then you can rotate the bond any number of degrees. If you look only at only that bond, you cannot see a difference after rotation.

Pi Bonds

A bond comes from the side-to-side overlap of p and d orbitals. The common type of bonds are $p\pi -p\pi ,p\pi -d\pi andd\pi -d\pi$

bonds have a nodal plane that is perpendicular to the lobes of the p and d orbitals and includes the bond axis. They do not have cylindrical symmetry. If you rotate the bond about the bond axis, you will see that the nodal plane has rotated as well.