Giant covalent structures

In giant covalent structures, all the atoms are linked to other atoms by strong covalent bonds.
These bonds must be overcome to melt or boil the substance, so giant covalent substances are solids with very high melting points.
Examples: diamond and graphite (forms of carbon) and silicon dioxide (silica, found in sand).

Diamond

In diamond, each carbon atom forms four covalent bonds with other carbon atoms in a rigid giant structure.
Diamond is very hard and has a very high melting point.
It does not conduct electricity, because it has no delocalised electrons.

In graphite, each carbon atom forms three covalent bonds, making layers of hexagonal rings.
There are no covalent bonds between the layers, only weak forces, so the layers slide over each other. This makes graphite soft and slippery.
Each carbon atom has one delocalised electron, so graphite conducts electricity and thermal energy, like metals.

Graphene is a single layer of graphite. It is very strong, light and conducts electricity, so it is useful in electronics and composites.
Fullerenes are molecules of carbon atoms with hollow shapes, based on hexagonal rings (sometimes with rings of five or seven atoms).
The first fullerene discovered was buckminsterfullerene, C₆₀, which is spherical.
Carbon nanotubes are cylindrical fullerenes with a very high length-to-diameter ratio. They are used in nanotechnology, electronics and strong materials, such as tennis rackets.

Giant covalent structure: A structure in which all the atoms are joined by strong covalent bonds.
Diamond: A form of carbon in which each atom forms four covalent bonds; very hard.
Graphite: A form of carbon in layers, in which each atom forms three covalent bonds; conducts electricity.
Graphene: A single layer of graphite, one atom thick.
Fullerene: A hollow molecule of carbon atoms, such as C₆₀.
Buckminsterfullerene: A spherical fullerene with the formula C₆₀.
Carbon nanotube: A cylindrical fullerene with a very high length-to-diameter ratio.
Silicon dioxide: A giant covalent compound (silica), found in sand.