Bonding

• Particle model assumptions

  That there are no forces between the particles

  That all particles in a substrate are spherical

  That all the spheres are solid
• Covalent bonding

  Where electrons are shared between non metals

  Single bond: Each atom shared one pair of electrons

  Double bond: Each atom shares two pairs of electrons
• Giant covalent

  Many billions of atoms bonded together with strong covalent bonds

  High melting point as it takes a lot of energy to break the strong bonds
• Small molecule

  Small numbers of atoms group into molecules, Strong covalent bonds between atoms, weak intermolecular forces between molecules

  Low melting point as only a small amount of energy is needed to break the weak intermolecular forces
• Large molecule

  Identical molecules joined together by strong covalent bond in a long chain, weak intermolecular forces between the chains

  Higher melting point than small molecules as the intermolecular forces are stronger
• Graphite 


  Giant covalent structure

  Each carbon bonds to 3 others, forms hexagonal rings in layers

  Layers can slide over each other because they arent covalently bonded, softer than diamond

  Delocalised electrons move and carry charges so graphite is a conductor of electricity
• Graphene: Single layer of graphite
• Fullerenes

  Hollow cages of carbon atoms bonded together in one molecule

  Can be arranged as a sphere or a tube

  Molecules held together by weak intermolecular forces, so can slide over each other

  Conducts electricity
• Spheres

  Buckminsterfullerene = first to be discovered

  Can be used as lubricants and in drug delivery
• Nanotubes


  Carbon atoms are arranged in cylindrical tubes

  High tensile strength (difficult to break when pulled) makes them useful in electronics
• How are ions formed?

  Atoms gaining or losing electrons, meaning the number of protons is diff to the number of electrons
• Ionic bonding

  When metal atoms react with non metal atoms they transfer electrons to the non metal atom

  Metal atoms lose electrons to become positive ions

  Non-metal atoms gain electrons to become negative ions
• Ionic structure

  Positive and negative ions are held together by the strong electrostatic force of attraction
• Ionic properties

  Melting points: High because the strong electrostatic force of attraction requires a lot of energy to break

  Conductivity: Solid ionic substances do not conduct electricity, melted or dissolved in water they do
• Delocalised electrons: Electrons that are free to move around
• Metal properties, Malleability, Conductivity, Melting points

  Malleability: Pure metals are malleable because the layers can slide over each other

  Conductivity: Metals are good conductors of electricity and thermal energy because of delocalised electrons

  Melting points: Metals have high melting points because the strong electrostatic force of attraction requires a lot of energy to break
• Alloy

  A mixture of 2 or more elements, at least one of which being a metal

  Useful as pure metals are too soft to use on their own
• Why dont most covalent structures conduct electricity?

  They don't have delocalised electrons