Carbon (OCR Gateway GCSE Chemistry: Combined Science)

• Carbon is located in Group 4 of the periodic table
• It has the ability to form four covalent bonds which allows it to form families of similar compounds that contain chains or rings 
• As a result, a large number of natural and synthetic organic compounds can be formed

• Allotropes are different forms of the same element
• The following allotropes all contain carbon atoms but due to the differences in bonding arrangements they are physically different 

Diamond  

• Each carbon atom bonds with four other carbons, forming a tetrahedron
• All the covalent bonds are identical, very strong and there are no intermolecular forces

Diagram showing the structure and bonding arrangement in diamond

• Diamond has the following physical properties:
  • It does not conduct electricity
  • It has a very high melting point
  • It is extremely hard and has a density of 3.51 g/cm3 - a little higher than that of aluminium

• All the outer shell electrons in carbon are held in the four covalent bonds around each carbon atom, so there are no freely moving charged particles 
• The four covalent bonds are very strong and extend in a giant lattice, so a very large amount of heat energy is needed to break the lattice
• Diamond ́s hardness makes it very useful for purposes where extremely tough material is required
• Diamond is used in jewellery and for coating blades in cutting tools
• The cutting edges of discs used to cut bricks and concrete are tipped with diamonds
• Heavy-duty drill bits and tooling equipment are also diamond tipped

Graphite   

• Each carbon atom in graphite is bonded to three others forming layers of hexagons, leaving one free electron per carbon atom
• These free electrons migrate along the layers and are free to move and carry charge, hence graphite can conduct electricity
• The covalent bonds within the layers are very strong, but the layers are attracted to each other by weak intermolecular forces, so the layers can slide over each other making graphite soft and slippery

Diagram showing the structure and bonding arrangement in graphite

• Graphite has the following physical properties:
  • It conducts electricity and heat
  • It has a very high melting point
  • It is soft and slippery and less dense than diamond (2.25 g/cm3)

• Graphite's weak intermolecular forces make it a useful material
• It is used in pencils and as an industrial lubricant, in engines and in locks
• It is also used to make inert electrodes for electrolysis, which is particularly important in the extraction of metals such as aluminium

Graphene 

• Graphene consists of a single layer of graphite which is a sheet of carbon atoms covalently bonded forming a continuous hexagonal layer
• It is essentially a 2D molecule since it is only one atom thick
• It has very unusual properties make it useful in fabricating composite materials and in electronics

Graphene is a truly remarkable material that has some unexpected properties

• Graphene has the following properties:
  • It is extremely strong but also amazingly light
  • It conducts heat and electricity
  • It is transparent
  • It is flexible

• Strength: It would take an elephant with excellent balance to break through a sheet of graphene
  • It is very strong due to its unbroken pattern and the strong covalent bonds between the carbon atoms. Even when patches of graphene are stitched together, it remains the strongest material out there

• Conductivity: It has free electrons which can move along its surface allowing it to conduct electricity
  • It is known to move electrons 200 times faster than silicon
  • It is also an excellent conductor of heat
• Flexibility: Those strong bonds between graphene’s carbon atoms are also very flexible

• Transparent: Graphene absorbs 2.3 percent of the visible light that hits it, which means you can see through it without having to deal with any glare
  • This gives it the potential to be used for making computer screens of the future

Fullerenes

• Fullerenes are a group of carbon allotropes which consist of molecules that form hollow tubes or spheres
• They are usually made up of carbon atoms arranged in hexagons but can also contain pentagons or heptagons
• The first fullerene to be discovered was buckminsterfullerene, also known as “buckyball”
• In this fullerene, 60 carbon atoms are joined together forming 20 hexagons and 12 pentagons which produce a hollow sphere that is the exact shape of a soccer ball
• Fullerenes can be used to trap other molecules by forming around the target molecule and capturing it, making them useful for targeted drug delivery systems
• They have a huge surface area and make very useful catalysts 
• Some fullerenes are excellent lubricants and are starting to be used in many industrial processes

Buckminsterfullerene was the first fullerene to be discovered as a component of soot. The 1996 Nobel Prize in Chemistry was jointly awarded for its discovery by teams at Rice University in Texas and the University of Sussex

Nanotubes

• Graphene can also be rolled into a cylinder to produce an interesting type of fullerene called a nanotube
• These have high tensile strength and are resistant to breaking or stretching
• As in graphene, nanotubes can also conduct electricity which makes them useful in composites and specialised materials, electronics and nanotechnology

Diagram showing the structure of nanotube produced from a rolled sheet of graphene