Options Material-Materials

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Options Material-Materials

• Crystals, Metals and Addition Polymers

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Crystals

• Crystals are formed by ions, atoms or molecules
  arranged in a regular geometric arrangement
  called a lattice.

Diamond Lattace
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William and Lawrence Bragg

• William and Lawrence Bragg used x-ray
  crystallography to determine the arrangement of
  particles within crystals.
• The arrangement of particles inside a crystal is
  often referred to as the crystal lattice.
• The unit cell is a structure that repeats
  throughout the unit lattice.

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Dorothy Hodgkin

• Dorothy Hodgkin worked out the structure of
  Vitamin B12 using x-ray crystallography and a
  computer.

• Hodgkin determined the three-dimensional
  structures of the following biomolecules
• cholesterol in 1937
• penicillin in 1945
• vitamin B12 in 1954
• insulin in 1969

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Amorphous

• A solid that does not have a crystal structure is
  said to be Amorphous.

Wax and Paraffin are amorphous
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Allotropes

• Allotropes are different physical forms of the
  same element. Carbon has 3 different allotropes,
  Diamond Graphite and Buckminsterfullerene.

Graphite
Buckminsterfullerene
Diamond
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Types of Crystals

• Crystals are classified into 4 types according to
  the type of particle that makes up the crystal.
• 1. Ionic Crystals
• 2. Molecular crystals
• 3. Covalent macromolecular crystal
• 4. Metallic Crystals

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Ionic Crystals

• Ionic crystals are hard and brittle solids.
• They possess high melting points.
• They are poor conductors of electricity, but
  their ability to conduct increases drastically in
  melt.
• Most ionic crystals dissolve in water since there
  is an attraction between the positive and
  negative ions and the polar water molecules

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Molecular Crystals

• Molecular crystals consist of such substances as
  N2, CCI4, I2 and benzene.
• Molecular crystals are very soft solids that
  possess low melting points.
• They are poor conductors of electricity.
• Generally, the molecules are packed together as
  closely as their size and shape will allow. The
  attractive forces are mainly van der Waals
  interactions

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Covalent Macromolecular Crystals

• Covalent crystals are hard solids that posess
  very high melting points.
• They are poor conductors of electricity.
• In covalent crystals, atoms are held together by
  covalent bonds.
• Well-known examples are two allotropic forms of
  carbon, diamond and graphite

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Buckminsterfullerene

• The other allotrope of carbon is
  buckminsterfullerene, named after the architect
  and inventor Richard Buckminster Fuller who
  created the geodesic domes
• Discovered in 1985
• Has 60 carbon atons and was nicknamed the bucky
  ball

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Metallic Crystals

• Individual metal atoms sit on lattice sites while
  the outer electrons from these atoms are able to
  flow freely around the lattice.
• Metallic crystals normally have high melting
  points and densities.
• Conduct Electricity
• Malleable and Ductile

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Summary of Crystals
Type Structural Unit Bonding Properties Examples
Ionic Positive and Negative ions Electrostatic Hard Brittle High mp. Conduct when solid or molten NaCl MgO NaN03
Non Polar Molecules Non Polar Molecules Weak Van der Waals Soft Low mp Non-conductors I2 CO2
Polar Molecules Polar Molecules Dipole Dipole Or Hydrogen Soft Low mp Poor conductors H2O NH3
Covalent macromolecular Atoms Covalent bonds Very hard High mp Non-conductors Diamond SiO2
Metallic Metallic ions Metallic High mp Good Conductors Cu Fe Na
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Polymers

• Addition Polymers
• An Addition Polymer is made by addition reactions
  between very many monomers (with double bonds) to
  form long molecules.
• Monomers are small molecules with double bonds
  that join together in large numbers by addition
  reactions to make large molecules.
• Examples of addition polymers include
• Poly(ethene) Low density(LDPE) and
  high density(HDPE)
• Poly(chloroethene)
• Poly(phenylethene)
• Poly(tetrafluorethene)
• Poly(propylene)

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POLYMERISATION OF ALKENES
EXAMPLES OF ADDITION POLYMERISATION
ETHENE
POLY(ETHENE)
PROPENE
POLY(PROPENE)
CHLOROETHENE
POLY(CHLOROETHENE) POLYVINYLCHLORIDE PVC
POLY(TETRAFLUOROETHENE) PTFE Teflon
TETRAFLUOROETHENE
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POLYMERISATION OF ALKENES
ADDITION POLYMERISATION
Process during polymerisation, an alkene
undergoes an addition reaction with itself
all the atoms in the original alkenes are used to
form the polymer long hydrocarbon chains are
formed
the equation shows the original monomer and
the repeating unit in the polymer
ethene poly(ethene)
MONOMER POLYMER
n represents a large number
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Polyethene

• Polyethene can be made in two ways, with branches
  (low density) and in straight chains (high
  density). Fawcett and Gibson discovered it in
  1933.LDPE consists of branched chains that do
  not pack closely together. Thus they are soft and
  flexible and used in bags and cling-film.HDPE is
  produced when ionic catalysts, called
  Ziegler-Natta catalysts are used at low pressure.
  The polyethene formed has no branching along the
  polymer chain. This allows the chains to be
  packed neatly as in a crystal. Compared with
  LDPE, HDPE is hard and less flexible and has a
  higher melting point. It is suitable for making
  bowls, buckets and baskets.

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Poly(chloroethane) (Polyvinyl Chloride PVC)

• Rigid plastic used to make window frames, gutters
  etc. (uPVC)
• The addition of plasticisers can turn PVC into a
  softer and more flexible product (pPVC). Used for
  raincoats, floor tiles, cable insulation.

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Polypropene (polypropylene)

• Polypropene has a similar structure to that of
  polyethene except that methyl groups are attached
  to every second carbon atom (head to head and
  head to tail polymerisation is possible).
• The presence of the methyl groups means that the
  groups of atoms arrange themselves in a kind of
  helical screw pattern along the length of the
  chain to cause the minimum interference with each
  other. This regular pattern means that
  polypropene is less flexible than polyethene and
  this also causes the polypropene to be harder and
  slightly stronger than polyethene. Polypropene is
  used in the manufacture of buckets, bowls, toys,
  laboratory sinks, etc.

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Polyphenylethene (polystyrene)

• Polyphenylethene is similar in structure to
  polyethene and polypropene except that phenyl
  groups are attached to every second carbon atom
  in the carbon chain.
• There are two types
• Rigid polystyrene is used to manufacture items
  like yoghurt pots, food containers, disposable
  drinking cups, flower pots, etc.
• Expanded polystyrene is used in insulating
  houses, ceiling tiles, egg boxes, packing for
  computers, etc.

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Polytetrafluoroethene (Teflon)

• Teflon is the trade name of the chemical
  polytetrafluoroethene discovered by Roy Plunkett
  of the Du Pont company in the USA. It is used in
  non-stick frying pans, space suits, artificial
  heart valves, etc. It was discovered in 1938.
• He found that this greasy white solid had
  remarkable properties it was extremely inert and
  was not affected by strong acids, bases or heat.
  He tried to dissolve it in various solvents and
  failed. A really unusual property of it was that
  it was very slippery. (It is listed in the
  Guinness Book of World Records as having the
  lowest coefficient of static and dynamic
  friction of any solid.)

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Recycling of Plastics

• The worlds production and use of plastic
  material has increased from less than 5 million
  tonnes in the 1950s to about 80 million tonnes
  today. Annual consumption of plastics in Western
  Europe is 28 million tonnes. In total, Western
  Europe produces some 11.5 million tonnes of
  plastics waste each year. An average European
  family of 4 throws away around 40 kg of plastics
  each year. There are a number of reasons why it
  is necessary to recycle plastics.
• (i) Plastic recycling saves natural
  resources.
• (ii) Plastic recycling makes economic sense.
• (iii) Recycling of plastics cuts waste disposal
  costs.
• (iv) Plastic recycling reduces litter.
• (v) Plastics recycling creates employment.

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Thermoplastics and Thermosetting plastics

• Not all plastics can be recycled
• Thermoplastics or Thermosoftening plastics can be
  softened and remolded a number of times.
• Thermosetting plastics cannot be
  remoulded-Bakelite

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Recycling of polystyrene

• Recycling of polystyrene contains five stages.
• 1. Sorting-polystyrene separated from other
  plastics.
• 2. Shedding-granulator
• 3. Washing
• 4. Drying-excess water removed.
• 5. Re-extrusion-melting followed by remoulding.