diamond & graphite

• Two substances made from the same element, that are in the same physical state, but that have different structures, are called allotropes.
• diamond has carbon atoms bonded to 4 other carbon atoms
• diamond

  
• graphite

  
• In diamond, each carbon atom is bonded to 4 other atoms via covalent bonds. 

  This forms a regular 3D lattice which is very strong, and has very high melting and boiling points.
• diamonds do not conduct electricity because since each carbon is bonded to 4 other carbon atoms there are no free electrons to carry charge
• graphite has its carbon bonded to 3 other carbon atoms

  
• Graphite is able to conduct electricity.

  This is because each carbon atom has one delocalised electron, which can move freely, and so is able to carry charge. 
• Graphite is a lot softer than diamond. 

  This is because the 2D layers of graphite stack on top of each other with only weak intermolecular forces holding them together.

  This means the layers can slide over each other, making graphite easier to break.