Topic 2 - Structure, Bonding and Smart Materials

• Nano titanium dioxide

  Uses -

  • Sunscreen - blocks harmful UV rays
  • Self-cleaning windows - breaks down dirt in sunlight
• Smart material

  Properties change with a change in surroundings including pH, temperature and light
• Shape memory polymer

  A form of plastic that can retain it's original shape when heated

  Uses -

  • Surgical stutters
  • Car bumpers
• Photochromic paint

  Changes colour with a change in light strength

  Use -

  • Transition lenses
• Thermochromic paint

  Changes colour with a change in temperature

  Uses -

  • T-shirts
  • Mugs
• Hydrogels

  Can swell and shrink up to 1000 times their volume depending on pH or temperature

  Uses -

  • Artificial snow - shrinks by heating and expands by adding water
  • Nappies - expands greatly when it becomes wet
  • Contact lenses
• Shape memory alloy

  Mixture of metals that retain their original shape when heated

  A mixture of nickel and titanium make up the alloy called NITI or nitinol

  • At low temperature it bends into any shape

  Use -

  • Stents - changes shape to open veins when at body temperature
• Concerns with the use of nano particles

  1. Small enough to enter blood stream through skin
  2. Long term effects are not known
• Metallic bonding

  • When metal atoms bond together
  • Electrons from the outer shell of the atoms are delocalised so they are free to move through the whole structure
  • Stronger metallic bonds are formed by sharing delocalised electrons
  • Strength of metallic bond is due to the force of attraction between the metal ions and the delocalised electrons
  • The delocalised electrons create a 'sea of electrons
• Nanosilver

  Properties -

  • Antibacterial and antifungal

  Uses-

  • Nano sliver plasters - kills bacteria to prevent infections
  • Antibacterial spray - kills bacteria on surfaces
• Nanoparticles

  • Size 1 to 100 nm (nanometers)
• Fullerene

  • A Giant Covalent structure
  • Used as a drug delivery system
  • Property: hollow centre
• Carbon Nanotube

  • A Giant Covalent structure
  • Used in micro circuits
  • Properties: same structure as graphite; conducts electricity
• Metallic properties

  • Conducts heat - the delocalised electrons and closely packed ions transfer energy through the structure by conduction
  • Malleable and ductile - layers of metal ions are able to slide over eachother when hammered or stretched
  • Conducts electricity - delocalised electrons carry electrical charge through the structure
  • High melting and boiling points - large amount of energy is needed to break the strong metallic bonds
• Simple molecular structures

  • Non-metals only
  • Low melting and boiling points due to the weak intermolecular forces between molecules
  • Doesn't conduct electricity as there are no free electrons to carry the electric current
• Graphite

  • A Giant Covalent structure (carbon atoms only)
  • Each carbon is bonded to 3 others therefore it conducts electricity as there are delocalised electrons between the layers which carry the charge
  • Used in pencils and lubricants as the layers can slide over eachother
• Diamond

  • A Giant Covalent structure (carbon atoms only)
  • Each carbon atom is bonded to 4 others so it does not conduct electricity as there is no free electrons to carry the electrical charge
  • Diamond is used in dril bits, glass cutting and gemstones as it is a hard natural resource
• Giant Ionic structures 


  • High melting and boiling points due to the strength of the electrostatic forces between the ions
  • Conducts electricity when dissolved or molten - ions are free to move to carry a charge
• Ionic bonding

  • Bonding between metal and non-metal atoms
  • Ionic bonds form when electrons transfer from a metal to a non-metal atom so both atoms can achieve full outer shells
  • A larger ionic charge produces stronger ionic bonds so more heat is required to break the bonds
• What is an Ion?

  • A charged particle which has different amounts of protons and electrons
  • Either a positive or negative charge
• Covalent bonding

  • Bonding between non-metal atoms
  • Covalent bonds form when the atoms share electrons so that both atoms achieve full outer shells
  • Double bonds = 2 pairs of electrons shared