Why is benzene so stable?

Benzene (C₆H₆) is a simple aromatic compound, which consists of a planar hexagonal ring of six carbon atoms, with each carbon being bonded to one hydrogen atom and two other carbon atoms. Carbon has four valence electrons, three of which are contained in three individual sp² hybridised orbitals and are involved in bonding with the three adjacent atoms. The fourth electron is contained in an unhybridised p-orbital and is able to become delocalised across the entire ring-structure and is shared between all six carbon atoms. Benzene has six carbon atoms in total and therefore six electrons become delocalised across the molecule, creating a ring of electron-density above and below the plane of the molecule. This ring of electron-density is known as a 'pi-cloud'. The delocalisation of electrons across the molecule means that benzene has relatively low energy, and isn't sufficiently electron-rich or electron-poor to react readily.