Giant Covalent Structures (Edexcel IGCSE Chemistry: Double Science)

• Giant covalent structures are solids with high melting points
• They have a huge number of non-metal atoms bonded to other non-metal atoms via strong covalent bonds
• These structures can also be called giant lattices and have a fixed ratio of atoms in the overall structure
• Two examples include diamond and graphite
• All giant covalent structures have high melting points because:

• • There are strong covalent bonds between atoms
  • These require lots of energy to overcome

Diamond

• Diamond and graphite are  allotropes of carbon
• Both substances contain only carbon atoms but due to the differences in bonding arrangements they are physically completely different
• In diamond, each carbon atom bonds with four other carbons, forming a tetrahedron
• Each covalent bond is very strong 

What are the properties of diamond?

• Diamond is very hard because:
  • Each carbon atom is covalently bonded to four other carbon atoms
  • The covalent bonds are very strong 
  • The hardness of diamond makes it useful for cutting tools
• Diamond has a high melting point because:
  • It has a giant covalent structure 
  • There are strong covalent bonds between atoms which need lots of energy to break 

The bonding and structure in diamond

Each carbon atom is bonded to four other carbon atoms

Graphite

• Each carbon atom in graphite is bonded to three others forming layers of hexagons, leaving one free electron per carbon atom

What are the properties of graphite?

• Graphite is soft and slippery
  • Each carbon atom is bonded to three other carbon atom forming layers 
  • The layers are free to slide over each other because there are only weak forces between the layers, not covalent bonds 
  • Graphite is used as pencil lead 
• Graphite can conduct electricity and heat   
  • Due to each carbon atom only forming three bonds, one electron from each carbon atom is delocalised 
  • The delocalised electrons are free to move 
  • Graphite is similar to metals in that it has delocalised electrons 
  • It is often used as electrodes during electrolysis 
• Graphite has a high melting point because:
  • It has a giant covalent structure 
  • There are strong covalent bonds between atoms which need lots of energy to break 

Bonding and structure in graphite

In graphite, each carbon is bonded to three other carbon atoms forming layers