Sigma bonds
- Formed by combining atomic orbitals or hybrid atomic orbitals
- Located within the plane of the molecule
- Circularly symmetric about the bond axis
- Head-on overlap (hybrid orbitals maximize overlap)
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Bonds - 1. Sigma Bonds
Sigma Bonds
- Sigma bonds are bonding molecular orbitals formed by combining atomic orbitals or hybrid atomic orbitals.
- They form single bonds within the plane of the molecule.
- Sigma bonds are circularly symmetric about the bond axis.
Let's learn how to visualize the circular symmetry of electron density of a sigma bond.
- Draw the nuclei of two atoms contained within electron spheres.
- Connect them with a bond axis and combine them.
- Indicate that when the two orbitals overlap, their electron density takes on an elliptical shape (like a symmetrical watermelon or football).
Then re-draw them as follows:
- Draw the two atoms enclosed in a three-dimensional ellipsoid shape.
- Next, slice through the center of the bond axis with a rectangular plane.
- Carve out the ellipsoid shape.
- Indicate that the cross-sectional plane is circular.
Key points
- Sigma bonds comprise a circular cross-sectional plane.
- All single bonds are sigma bonds.