Giant Covalent structures

Silicon

• Each silicon atom is covalently bonded to four others

• Tetrahedral geometry

• Bond angle of approximately 109.5

Silicon (IV) oxide

• Also known as silicon dioxide

• Main component of sand

• Each silicon atom is covalently bonded to four oxygen atoms 

• Each oxygen atom is bonded to two silicon atoms 

• Tetrahedral geometry

• Structure extends in all directions

• The empirical formula is SiO₂ because the structure is based on a repeating ratio rather than discrete molecules. 

Diamond

• Each carbon atom is covalently boned to four others

• Tetrahedral geometry

• Bond angles of 109.5

• Diamonds are very hard because breaking the structure requires breaking many strong covalent bonds

• Does not conduct electricity because all four outer electrons on each carbon atom are bonded.

Graphite 

• Each carbon atom is covalently bonded to three others in hexagonal rings arranged in flat layers

• Molecular geometry is trigonal planar 

• Bond angle of 120 

• Graphite conducts electricity because the fourth outer electron of each carbon is delocalised and moves freely between the layers

• Graphite is soft and slippery because the layers are held together by weak intermolecular forces and can slide over each other 

Buckminsterfullerene

• A molecular form of carbon made of 60 atoms boned in a spherical structure

• Each carbon forms three covalent bonds, creating a pattern of interlocking hexagons and pentagons

• The remaining electron on each carbon is delocalised, allowing limited, but some electron movement, hence it is a semiconductor

Graphene

• A single layer of carbon atoms arranged in a hexagonal lattice

• Each carbon atom is bonded to three others with trigonal planar geometry

• Bond angle of 120

• Conducts electricity because the fourth outer electron of each carbon is delocalised

• The structure of graphene is two-dimensional, and is one atom thick

• Strong and flexible