Sigma Bond

• Electrons are not static; rather, they move around the nucleus of the atom, which is represented as a pattern similar to a figure-eight. When atoms bind, it forms a line between the two nuclei in the bond called the internuclear axis. In a sigma bond, two atoms share an electron in a head-to-head manner where the electron is found around the internuclear axis. Sigma bonds create single bond and one bond in a multiple bond.
  
  

Pi Bonds

• Pi bonds make up the remaining bonds in a multiple bond. In a pi bond, the electron is shared between atoms in a side-to-side manner where the electron is found above or beyond the internuclear axis. Pi bonds are weaker than sigma bonds. Molecules with one sigma bond and one pi bond are called double bonds while molecules with one sigma bond and two pi bonds are triple bonds.
  
  

Delocalization

• In many cases, the multiple bond is fixed between two atoms. In some cases, the multiple bond will rotate around the molecule. For example, benzene is represented as six carbon atoms arranged in a hexagon with alternating single and double bonds around the ring. However, the electrons actually rotate around the ring, so that the double bond is constantly moving. This is called delocalization or delocalized electrons.
  
  

Representation

• Molecules are typically represented on paper using the symbol of the atoms from the periodic table and lines to represent bonds. For example, two hydrogen atoms bonded together are represented as H-H. A multiple bond is represented with multiple lines. For example, two carbon atoms sharing a double bond are represented as C=C.