Which form of carbon involves flat layers of bonded carbon atoms?

• A. Diamond
• B. Graphite
• C. Fullerene
• D. Nanotube

Answer: (B)

Carbon can form different structures called allotropes, each with its own bonding arrangement. The form with flat layers of bonded carbon atoms is graphite, because carbon atoms bond in two-dimensional planes to make graphene sheets. Within a sheet, each carbon forms strong covalent bonds with three neighbors, creating a hexagonal pattern. The sheets stack on top of each other and are held together by weaker forces between layers, so the layers can slide past one another easily and be separated. This layered structure gives graphite its characteristic properties, like being able to leave a mark on paper and its lubricating quality. In contrast, diamond forms a three-dimensional network where each carbon bonds to four others, making a very hard solid; fullerenes are spherical cages of carbon, and nanotubes are rolled-up graphene sheets that form hollow cylinders.