Very large molecules
Graphene
grapheneA form of carbon consisting of a single layer of carbon atoms joined together in hexagonal rings. is an allotropesAllotropes are different forms of the same element in the same state. For example, diamond and graphite are allotropes of carbon. of carbon. Its structure resembles a single layer of graphiteA form of pure carbon in which all the atoms are bonded to three others in giant sheets which can slide over each other.. Graphene has a very high melting pointThe temperature at which a solid changes into a liquid as it is heated. and is very strong because of its large regular arrangement of carbon atomThe smallest part of an element that can exist. joined by covalent bondA bond between atoms formed when atoms share electrons to achieve a full outer shell of electrons.. Like graphite, it conductTo allow electricity, heat or other energy forms to pass through. electricity well because it has delocalisedElectrons that are not associated with a particular atom, eg in a metal, outer electrons can be free to move through the solid. electronSubatomic particle, with a negative charge and a negligible mass relative to protons and neutrons. that are free to move across its surface.
Fullerenes
A fullerenesMolecules of carbon with hollow shapes. Their structures are based on hexagonal rings of carbon atoms. is a molecularRefers to a substance made up of molecules, so it contains small groups of atoms, of a set size, held together by covalent bonds. allotrope of carbon. Two examples of fullerenes are nanotubesLong cylindrical molecules made from carbon atoms joined together by covalent bonds. and buckyballsMolecules comprising carbon atoms joined together to form spherical or nearly spherical hollow structures..
Nanotubes
A nanotube resembles a layer of graphene, rolled into a tube shape. Nanotubes have high tensile strengthThe tension a material can withstand without breaking., so they are strong in tensionPulling force exerted by each end of an object such as a string or rope. and resist being stretched. Like graphene, nanotubes are strong, and they conduct electricity because they have delocalised electrons.
Buckyballs
Buckyballs are spheres or squashed spheres of carbon atoms. They are made up of large molecules so are not classed as giant covalent structureA structure in which very large numbers of atoms are joined together by covalent bonds in a regular network.. Weak intermolecular forcesWeak attractive forces between molecules. When a simple molecular substance melts or boils, it is the intermolecular forces that are broken (not the covalent bonds in each molecule). exist between buckyballs. These need little energyThe capacity of a system to do work or the quantity required for mechanical work to take place. Measured in joules (J). For example, a man transfers 100 J of energy when moving a wheelbarrow. to overcome, so substances consisting of buckyballs are slippery and have lower melting points than graphite or diamondA form (allotrope) of pure carbon in which all the atoms are bonded to four others in a giant tetrahedral network structure which is very strong. Diamond is the hardest known natural substance, has a very high melting point and does not conduct electricity..