yr11 applied science unit 3

• Tennis racquet frame material

  Racquets were made of laminated wood up until the late 1960s when the first racquets using steel were introduced. In the mid-1970s steel was replaced with aluminium but these were in turn replaced by racquets made from graphite.
• Decisions need to be made about the best material to use for applications in every walk of life
• Material scientists need to understand how materials are held together if they are to develop new materials with properties that make them suitable for a purpose
• This means they need to understand bonding
• Ionic bonding


  Transfer of electrons from a metal to a non-metal to form ions of opposite charge. Strong electrostatic attraction between oppositely charged ions holds the ions in a close, regular structure.
• Covalent bonding


  Pairs of electrons are shared between atoms to form molecules. Strong covalent bonds in the molecules, weak forces between molecules.
• Ionic bonding


  1. Metal loses electrons to form positive ions

  2. Non-metal gains electrons to form negative ions

  3. Oppositely charged ions held by strong electrostatic attraction
• Ionic charge and position in the periodic table

  • Group 1 metals +1
  • Group 2 metals +2
  • Group 3 metals +3
  • Group 4 elements do not tend to form ions
  • Group 5 non-metals -3
  • Group 6 non-metals -2
  • Group 7 non-metals -1
• Structure of ionic compounds


  • Giant structures made up of large numbers of ions
  • Each positive ion surrounded by negative ions, each negative ion surrounded by positive ions
  • Strong electrostatic forces between oppositely charged ions
• Properties of ionic compounds


  • High melting and boiling points
  • Conductive when liquid, non-conductive when solid
  • Most are soluble in water
• Covalent bonding


  Atoms share pairs of electrons to obtain full outer shells
• Dot and cross diagrams showing covalent bonding


  • Two chlorine atoms sharing a pair of electrons
  • Oxygen atom sharing two pairs of electrons with two hydrogen atoms
  • Nitrogen atom sharing three pairs of electrons with another nitrogen atom
• Properties of covalent compounds

  • Strong covalent bonds within molecules, weak forces between molecules
  • Low melting/boiling points as only weak intermolecular forces need to be broken
• Graphene is a one-atom thick sheet of carbon atoms bonded into a honeycomb lattice
• Properties of graphene


  • Very strongly bonded carbon atoms, making it the strongest material yet made
  • About 200 times stronger than steel
• Graphite


  • Made of many layers of graphene stacked together
  • Strong bonds within layers, weak bonds between layers allowing layers to slide over each other
• Carbon nanotubes


  • Long molecular-scale tubes of carbon, with hexagonal rings of bonded carbon atoms
  • Very strong due to covalent bonding within tubes
• Carbon nanotubes may be strong and light enough to be used in a space elevator cable
• Fullerenes are a large class of allotropes of carbon made of balls and 'cages' of carbon atoms
• Carbon nanotubes


  Tubes of carbon bonded in hexagonal rings, formed by curling a layer of graphite or graphene
• Carbon nanotubes have been constructed with lengths up to 132,000,000 times their diameter
• Carbon nanotubes


  • They are a very strong material due to the strong covalent bonding within each tube
  • They have many possible applications, e.g. bullet proof vests, making lightweight and strong sports equipment
• An elevator into space could be made from Earth to a satellite using cables made of a very light and strong material
• Fullerenes


  A large class of allotropes of carbon made of balls and 'cages' of carbon atoms
• Buckminster fullerene


  A type of fullerene molecule with 60 carbon atoms arranged in a hollow sphere, with each carbon bonded to three neighbouring carbon atoms in rings of 5 or 6 carbon atoms
• Fullerenes


  • Their structure allows them to be used for drug delivery into the body, as lubricants and as catalysts
• Carbon is in group four and is four electrons short of a full shell
• In the structures examined, carbon shares three of the four electrons to make strong covalent bonds, and the fourth electron is a free (or delocalised) electron that can move throughout the layer
• The electrical properties of these carbon structures are due to the free (or delocalised) electrons
• Uses of graphene, graphite and carbon nanotubes based on electrical properties


  • Graphene: low energy light bulbs, lightweight flexible display screens, solar cells
  • Graphite: electrodes in industrial processes
  • Carbon nanotubes: electronics industry
• Diamond is a giant molecular structure where each carbon atom is covalently bonded to four other carbon atoms in a three-dimensional structure
• Diamond does not conduct electricity because there are no free electrons or ions
• Uses of diamond


  • Drill bits which cut through rocks or other hard materials
  • Cutting tools
  • Jewellery due to its ability to sparkle and reflect light when cut correctly
• Metals


  Pure metals are made of one kind of atom and typically have high electrical and thermal conductivities, are hard and strong
• Alloys


  Mixtures of two or more elements, one of which is a metal, with properties that make them more useful than pure metals
• Polymers


  Generally organic compounds based upon carbon and hydrogen, very large molecular structures, usually low density and not stable at high temperatures, with lower strength, stiffness, and melting temperatures than metals and ceramics
• Ceramics


  Inorganic solids that have been shaped and then hardened by heating to high temperatures, hard brittle compounds with very high melting points, low thermal conductivity and high resistance to chemical attack
• Composites


  Made when two or more materials with different properties are combined to produce a new material, where the physical and chemical properties of each of the constituent materials remain distinct in the new material
• The bonding between atoms in a metal is best described as closely packed positive metal ions in a 'sea' of delocalised (free) electrons
• General properties of metals


  • High thermal conductivity (good conductor of heat)
  • High electrical conductivity (good conductor of electricity)
  • Dense
  • High melting and boiling point
  • Strong
  • Hard
  • Malleable and ductile
  • Lustrous (shiny)