Bonding, Structure and Properties of Matter

• This is unit 2 for GCSE chemistry for AQA, for both combined science and triple science students
• The triple science content is labeled in the video, as is any higher content that is needed
• Chemical bonds


  Bonds between atoms in an element or a compound
• Strong chemical bonds


  • Ionic
  • Covalent
  • Metallic
• Ionic bonding


  Happens between metal and non-metal atoms, involves the transfer of electrons, and is caused by oppositely charged ions
• Covalent bonding


  Happens between non-metal and non-metal atoms, involves the sharing of pairs of electrons
• Metallic bonding


  Happens in metal elements and alloys, involves sharing delocalized electrons between the atoms
• Ionic bonding


  1. Metal atoms lose electrons and become positively charged ions

  2. Non-metal atoms gain electrons and become negatively charged ions
• Ionic bonding in sodium chloride

  • Sodium atom
  • Chlorine atom
• Sodium ion


  Positive charge, full outer shell
• Chloride ion


  Negative charge, full outer shell
• Electrostatic force of attraction

  Between oppositely charged ions
• Ionic compounds


  • Giant lattice structures
  • Held together by strong electrostatic forces of attraction in all directions
• Properties of ionic compounds

  • High melting and boiling points
  • Cannot conduct electricity in solid form
  • Can conduct electricity when dissolved in water or molten
• Covalent bonding


  Atoms share pairs of electrons to gain a stable arrangement (full outer shell)
• Covalent compounds/substances


  • Chlorine
  • Hydrogen chloride
  • Water
  • Oxygen
  • Nitrogen
  • Ammonia
  • Methane
• Substances made of small molecules

  • Relatively low melting and boiling points
  • Weak intermolecular forces of attraction between molecules
• Intermolecular forces


  Increase with molecule size
• Substances made of small molecules

  • No overall electric charge
  • No free electrons to move around, so cannot conduct electricity
• Polymers


  • Have very large molecules
  • Bonds between atoms are covalent and strong
  • Intermolecular forces are relatively strong
• Polymers


  • Solid at room temperature due to relatively strong intermolecular forces
• Giant covalent structures


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


  • Diamond
  • Graphite
  • Silicon dioxide (silica)
• Diamond


  • Each carbon atom forms 4 covalent bonds with other carbon atoms
  • No free electrons, so cannot conduct electricity
• Graphite


  • Each carbon atom forms 3 covalent bonds
  • Layers held together by weak forces, allowing layers to slide over each other
  • Has free/delocalized electrons
• Silicon dioxide (silica)


  • Each silicon atom covalently bonded to 2 oxygen atoms
  • No free electrons, so cannot conduct electricity
• Diamond


  Cannot conduct electricity
• Graphite


  • Structure made of carbon atoms, each forming 3 covalent bonds to form layers of hexagonal rings, with weak forces of attraction between the layers allowing them to slide over each other easily, making graphite soft and slippery
  • Contains free or delocalized electrons that can flow and conduct electricity
• Silicon dioxide (silica)


  Hard structure with each silicon atom covalently bonded to 2 oxygen atoms, no free electrons so cannot conduct electricity
• Diamond, graphite and silicon dioxide have high melting and boiling points due to strong covalent bonds
• Metallic bonding


  Atoms/ions arranged in a lattice structure, with delocalized electrons holding the metal ions together and allowing conduction of electricity and heat
• Alloys


  Harder than pure metals because the layers are distorted by other metal/non-metal atoms, preventing the layers from sliding over each other easily
• Graphene


  Single layer of graphite, with 3 electrons per carbon atom able to flow and conduct electricity, high melting point
• Buckminster fullerene (C60)


  Spherical molecule made of hexagons and pentagons of carbon atoms, poor electrical conductor but good lubricant due to ability to roll
• Carbon nanotubes


  Cylindrical tubes of hexagonal carbon rings, high length to diameter ratio, can conduct electricity due to delocalized electrons
• Potential uses of graphene, nanotubes, fullerenes

  • Strength, high melting points, ability to conduct electricity, drug delivery, lubrication
• Solid


  Particles close together in rows and columns, vibrating in fixed positions
• Liquid


  Particles in less regular arrangement, free to move around
• Gas


  Particles far apart, moving randomly at different speeds
• Changes of state


  1. Melting (solid to liquid)

  2. Boiling (liquid to gas)

  3. Condensing (gas to liquid)

  4. Freezing (liquid to solid)