pi bond locations

[Sharon Rodriguez 3H]

How would you know if the pi bonds of a molecule are perpendicular to each other vs. parallel? In the case of H2CCCH2, the C=C pi bonds are parallel to each other but in H2CCCH2 the C=C pi bonds are parallel. Would we have to know this for test 2?

[Sarah Blake-2I]

I do not think we need to know this for the test. Just know what pi and sigma bonds are and how they relate to the molecule in terms of strength and properties (pi bonds make the molecule rigid). Their location and whether or not they are parallel or perpendicular shouldn't matter for the test, but if you did have to draw the shape of the molecule, then it would come down to figuring out the lowest formal charge for the atoms, which will determine where the single, double, and triple bonds are.

[Jainam Shah 4I]

Sigma bonds lie along the internuclear axis meaning the internuclear axis passes through two overlapping orbitals. This means they are no nodal planes and the atoms can rotate freely. For pi bonds the orbital lie perpendicular to the internuclear axis and there is a nodal plane so they cannot rotate.

[Veronica_Lubera_2A]

Single bond: 1 sigma bond
Double bond: 1 sigma, 1 pi bond
Triple bond: 1 sigma, 2 pi bonds

Sigma bonds form when orbitals overlap end to end.
Pi bonds form when orbitals overlap side by side.