Pi bonds
- Formed from parallel overlap of adjacent p orbitals
- Do not form single bonds
- Located above and below the plane of the molecule
- Side-by-side overlap of p orbitals (weaker than head-on overlap)
Bonds - 3. Pi Bonds: Overlap
Pi Bonds
- Pi bonds are bonding molecular orbitals formed from parallel overlap of adjacent p orbitals.
- Pi bonds do NOT form single bonds.
- A single pi bond is found above and below the plane of the molecule.
- The overlap of pi bonding is weaker than the head-on overlap of sigma bonding.
Hybrid orbitals maximize head-on overlap with the atomic orbital to increase bond strength and stability.
- We see that there is more constructive interference between the enlarged lobe of the sp2 orbital and the 1s orbital than between the 2px orbital and the 1s orbital.
- Hybridization results in maximal overlap of electron densities of the sigma bond.
We illustrate the interaction between the pz orbitals that form the pi bond in ethylene.
- We draw both the energy level and also the shape of two vertically oriented 2p orbitals of two carbon atoms, each with its top lobe shaded the same color.
- The pi bonding molecular orbital is at a lower energy level.
- We show a node along the bonding axis (since the lobes of each orbital are opposite phase).
- Its shape is two 2p orbitals side-by-side with opposite orientations.
We add the electrons to each orbital:
- Each 2p orbital has 1 electron of "up" spin
- Both electrons are paired together in the bonding orbital.