▎ 摘　　要

Graphene is a new and hot research topic due to properties previously not observed on the nanoscale. These properties make graphene a promising candidate for new devices. However, graphene is not soluble, and this property limits its processability. Therefore, chemical functionalization is needed. This short review summarizes the covalent chemical reactions that have been performed on individual graphene sheets - the production of graphene oxide with subsequent transformation to graphene, the covalent modification of graphene oxide functional groups and the surface chemistry of the aromatic rings of graphene sheets.