Metallic Structures and New Materials

Metallic Structures and New Materials

1. Metal Properties are all due to the sea of electrons

   • Metals also consist of a giant structure
   • Metallic bonds involve the all-important 'free electrons' which produce all the properties of metals. These delocalised (free) electrons which produce all the properties of metals. These electrons come from the outer shell of every metal atom in the structure
     • These electrons are free to move through the whole structure and so metals are good conductors of heat and electricity
     • These electrons also hold the atoms together in a regular structure. There are strong forces of electrostatic attraction between the positive metal ions and the negative electons
     • They also allow the layers of atoms to slide over each other

2. Alloys are Harder than pure metals

   • Pure metals often arent quite right for certain jobs. So scientists mix two or more metals together creating an alloy with the properties they want
   • Different elements have different sized atoms. So when another metal is mixed with a pure metal the new metal atoms will distort the layers of metal atoms making it more difficult for them to slide over each other. So alloys are harder

3. You should be able to easily identify most substances just by the way they behave

4. Smart materials have some weird properties

   • Smart materials behave differently depending on the conditions e.g. temperature
   • Nitinol is a shape memory alloy
     • Its handy for glasses frames. If you accidentally bend them you can just pop them into a bowl of hot water and theyll jump back into shape

5. Nanoparticles

   • Really tiny particles 1-100 nanometers are called nanoparticles
   • Nanoparticles contain roughly a few hundred atoms
   • Nanoparticles include fullerenes. There are molecules of carbon shaped like hollow balls or closed tubes. The carbon atoms are arranged in hexagonal rings. Different fullerenes contain different numbers of carbon atoms
     • Fullerenes can be joined together to form nanotubes. Tiny hollow carbon tubes a few nanometres across
     • All those covalent bonds make carbon nanotubes very strong. They can be used to reinforce graphite in tennis rackets
   • A nanoparticle has very different properties from the bulk chemical that its made from e.g. fullerenes have different properties from big lumps of carbon
   • Nanoscience.
     • Many new uses of nanoparticles
       • They have a huge surface area to volume ratio so they could help make new industrial catalysts
       • You can use nanoparticles to make sensors to detect one type of molecules and nothing else. Highly specifc sensors are already being used to test water purity
       • Nanotubes can be used to make stronger, lighter building materials
       • New Cosmetics e.g. sun tan cream. The small particles do their job but dont have leave white marks on the skin
       • Nanomedicine. The tiny fullerenes are absorbed more easily by the body than most particles. This means they could deliver drugs right into cells where there needed
       • New lubricant coatings are being developed using fullerenes. These coatings reduce friction a bit like ball bearings and could be used in all sorts of places from artificial joints to gears
       • Nanotubes conduct electricity so they can be used in tiny electric circuits for computer chips

6. Polymers

   • Forces between molecules determine the properties of plastics
     • Strong covalent bonds hold the atoms together in long chains. But its the bond between the different molecule chains that determine the properties of plastics
     • Weak Forces
       • Individual tangled chains of polymers held together by weak intermolecular forces are free to slide over each other
       • Thermosoftening Polymers dont have cross linking between chains. The forces between chains are really easy to overcome so its dead easy to melt the plastic. When it cools the polymer hardens into a new shape. You can melt these plastics and remould them as many times as you like
     • Strong Forces
       • Some plastics have stronger intermolecular forces between the polymer chains called crosslinks that hold the chains firmly together
         • Thermosetting Polymers have crosslinks these hold the chains together in a solid structure. The polymer doesnt soften when its heated. Thermosetting polymers are the tough guys of the plastic world. There strong, hard and rigid
   • How you make a polymer affects its properties
     • The starting materials and reaction conditions will both affect the properties of a polymer.
     • Two types of polythene can be made using different conditions
       • Low density (LD) polythene is made by heating ethene to about 200 under high pressure. Its flexible and is used for bags and bottles
       • High density (HD) polythene is made at lower temperature and pressure (with a catalyst). Its more rigid and is used for water tanks and drainpipes

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