Sigma σ and Pi π bond

Different kinds of bonds result from the different ways the orbitals can overlap in space. The kind of symmetry the resulting bond has with the bond axis, (an imaginary line that connects the centers of the bonded atoms) determines what kind of bond is formed:

·   Sigma bond: When orbitals overlap in a way that is completely symmetrical with the bond axis, an σ bond (sigma bond) is formed. Sigma bonds form when s or p orbitals overlap in a head-on manner. Single bonds are usually sigma bonds.

·   Pi bond: When orbitals overlap in a way that is symmetrical with the bond axis in only one plane, a π bond (pi bond) is formed. Pi bonds form when adjacent p orbitals overlap above and below the bond axis.

Sigma bonds are stronger than pi bonds because the electrons within sigma bonds lie entirely between the two atomic nuclei, simultaneously attracted to both. A double bond is one sigma bond and one pi bond, and a triple bond is one sigma bond and two pi bonds.