1g) covalent bonding

• Covalent bond

  Bond formed between atoms by the sharing of a pair of electrons
• Covalent bonding

  • Occurs in most non-metallic elements and in compounds of nonmetals
  • Bonds between atoms are strong
• Covalent bonds

  Result of electrostatic attraction between the positive nuclei of the atoms and the pairs of negative electrons that are shared between them
• Using dot-and-cross diagrams to represent covalent bonds

  1. In diatomic molecules

  2. In inorganic molecules

  3. In organic molecules containing up to two carbon atoms

  
• Inorganic molecules

  • Water
  • Ammonia
  • Carbon dioxide
• Organic molecules containing up to two carbon atoms

  • Methane
  • Ethane
  • Ethene

  
• Substances with simple molecular structures

  Usually gases or liquids with low boiling and melting points
• Intermolecular forces of attraction

  Forces between molecules
• Relative molecular mass of substances with simple molecular structures

  Melting and boiling points increase with increasing relative molecular mass
• Substances with giant covalent structures

  • Solids with very high melting points
  • All atoms linked by strong covalent bonds
• Diamond

  • Each carbon atom joined to 4 other carbons covalently
  • Very hard, high melting point, does not conduct electricity
• Graphite

  • Each carbon atom covalently bonded to 3 other carbons, forming layers with no covalent bonds between layers
  • Layers can slide over each other, making graphite soft and slippery
  • One electron from each carbon atom is delocalised, allowing graphite to conduct electricity
• Graphene

  Single layer of graphite, has properties useful in electronics and composites
• Fullerenes

  • Molecules of carbon atoms with hollow shapes, based on hexagonal rings of carbon atoms but may also contain rings with five or seven carbon atoms
  • First discovered fullerene was Buckminsterfullerene (C60) with a spherical shape

  
• Carbon nanotubes

  Cylindrical fullerenes with very high length to diameter ratios, useful for nanotechnology, electronics and materials
• Covalent compounds do not usually conduct electricity, except for graphite and graphene