What is a characteristic of sigma bonds?

A sigma bond is formed by the head-on overlap of atomic orbitals, which typically includes s-s, s-p, and p-p overlaps. The key characteristic of sigma bonds that distinguishes them is that they allow for free rotation around the bond axis due to this type of overlap. This rotational freedom stems from the symmetrical nature of sigma bonds; as the electron density is distributed along the bond axis, rotation does not affect the overlap of the orbitals involved.

In contrast, the other options highlight common misconceptions. For example, while double bonds consist of one sigma bond and one pi bond, sigma bonds themselves are not limited to double bonds—they can also exist in single bonds. Additionally, sigma bonds are generally stronger than pi bonds due to the extent of orbital overlap, contrary to the idea that they are always weaker. Lastly, while pi bonds do involve the overlap of p orbitals, sigma bonds can form from various types of orbital overlap, including hybrid orbitals or s orbitals, making this statement incomplete and inaccurate in describing sigma bonds specifically.