What are some common mistakes students make with pi bonds?
Here are some of the mistakes I can think of when dealing with pi bonds:
More on this here: http://socratic.org/questions/why-are-pi-bonds-weaker-than-sigma-bonds
The difference between a sigma and a pi bond lies in the orientation of the orbitals that come together, i.e. whether or not they overlap head-on or side-on. Some examples of sigma bonds:
Two p-orbitals form a pi bond when they overlap side-on (are parallel to each other), like this:
Pi bonds only come in combination with sigma bonds, you can't have two atoms bonded solely by a pi bond. The pi bond present in a double bond strenghtens the bonds between the atoms by adding to the sigma bond. The same can be said for the two pi bonds present in a triple bond.
Always remember that a pi bond, which of course includes the above and below planes, can hold no more than 2 electrons.
SImply put, no they do not. Pi bonds inhibit free rotation in molecules because of their specific overlap.
Pi bonds are always formed from unhybridized orbitals, more often than not from unhybridized p-orbitals (d-orbitals can also form pi bonds as part of the metal-metal multiple bonding).