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Sigma and Pi bonds are formed by the overlap of atomic orbitals. Sigma bonds are formed by end-to-end overlapping and Pi bonds are when the lobe of one atomic orbital overlaps another. These orbitals are the same orbitals that we talked about in previous lectures (s, p, d, etc.).
Something to add on is that all single bonds are sigma bonds, all double bonds have one sigma and one pi bond, and all triple bonds have one sigma and two pi bonds and so on (all have one sigma, the rest are pi bonds). The sigma bonds allow the molecule to rotate, but the pi bonds are rigid and lock the molecule into place so that it is unable to rotate.
Sigma bonds have their electron density along the bond axis and cylindrical in shape which allow for rotation. Pi bonds have their electron density above and below the bond axis. Their orbitals overlap side by side which makes them rigid, trying to rotate that bond would result in breaking that bond.
Meigan Wu 3I wrote:Also, sigma bonds are made from hybridized orbitals and pi bonds are made from unhybridized orbitals.
What happens when a d orbital is involved in hybridization? Does that affect the shape in any way?
sigma bonds involve a single overlap, such as when two s orbitals overlap, or one s overlaps with a p orbital. pi bonds involve a double overlap, such as when two p orbitals overlap side by side, so that they are inflexible. this is why pi bonds are stronger
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