Describe the shape of, and bonding in, a molecule of benzene and explain why benzene does not readily undergo addition reactions.
Benzene is a planar, cyclical, hexagonal molecule, with the molecular formula C6H6. It consists of a ring of 6 carbon atoms with alternating single bonds and double bonds. The length of the bonds is equal and the angle between two C-C bonds is 120 degrees.
This is due to the delocalization of electrons in benzene. Pi bonds are formed from the p orbitals of the carbon atoms. When we have alternating pi bonds, if the three or more pi orbitals are in the same plane, the electrons can freely move between orbitals thus leading to a structure where every bond in the structure of benzene is a mix between a single bond and a double bond, leading to every bond being equivalent and having the same length. This delocalization suits the electrons well, since they like to be free instead of bound to a single bond, and lowers the overall energy of the molecule.
Addition reactions to benzene would eliminate one or more pi bonds, thus leading to a structure where the delocalization of electrons is more limited or even completely missing (due to there being less pi orbitals to move to and from). This raises the overall energy of the molecule and is as such difficult to achieve.
