Graphene is a single-atom-thick planar sheet of sp2-bonded carbon atoms perfectly arranged in a honeycomb structure that forms a large polyaromatic molecule of semiinfinite size. The unique structure endows graphene with interesting and extraordinary properties including room temperature high electron mobility, room temperature quantum Hall effect, a tunable bandgap, high transparency, strong mechanical strength, and good chemical/physical stability. The electronic properties of a material are always determined by its electronic structure. The electron configuration of carbon atoms is 1s22s22p2, where the outer shell consisting of 2s22p2 can hybridize to form different hybrid orbitals, resulting in various carbon nanomaterials. The electronic properties of a material are always determined by its electronic structure. Two approaches, doping and functionalization, are often utilized to achieve desired chemical properties of graphene. The chemical properties of graphene are considered to be similar to those of benzene and polycyclic aromatic hydrocarbons as they share analogous structures.