Chemistry Unit 2- Structure and Properties

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Giant Ionic Structures/ Simple Molecules

  • Ionic compounds have giant structures many strong electrostatic forces hold ions together.
  • Solids at room temperature. A lot of energy needed to break bonds and melt the solids.
  • High melting and boiling points.
  • When ionic compound melted the ions are free to move. Now can carry electrical charge, ergo liquids conduct electricity.
  • Ionic compounds can dissolve in water as water molecules can split up the lattice.
  • Ions are free to move in the solution so can conduct electricity.
  • Atoms within a molecule are held together by strong covalent bonds.
  • The bonds only act between the atoms within the molecule, so simple moleculeshave little attraction for each other.
  • Substances made of simple mols have kinda low melting and boiling points
  • They don't conduct electricity as mols have no overall charge so can't carry electrical charge.
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Giant Covalent Structure

  • Atoms of some elements can form several covalent bonds, these can join into GCS's (or macromolecules)
  • Every atom in the structure is joined to other atoms but strong CB's
  • Takes a large amount of energy to break down lattice so substances have very high melting points.
  • Diamond is a form of carbon, it has a regular 3-D giant structure. Each carbon atom is CB'd to 4 other carbon atoms.
  • Makes diamonds hard and transparent
  • Compound sillicon dioxide (silica) has a similar structure
  • Graphite is a form of carbon , atoms are CB'd to 3 other carbon atoms in giant 2-D.
  •  No CB's between layers so they slide over each other, making it slippery and grey.
  • One electron from each carbon atom is delocalised like in metal, can conduct
  • Fullerenes are large molecule formed from the hexagonal rings of carbon atoms. They join to from cage like shapes with different amounts of carbon atoms that may be nano sized.
  • Scientists use fullerenes for drug delivery into body, lubricants, catalysts and reinforcing materials.
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Giant Metallic Bonding & Nanoscience

  • Metal atoms are in layers. When force applied, layers slide over each other.
  • Can move into new position without breaking apart, so metal bends into new shape.
  • Metals are useful for making wires, rods and sheet metals.
  • Alloys are mixtures of metals or metals with other elements.
  • Different sized atoms in the mixture distort the layers in the metal structure so harder to slide over each other. Alloys are harder than pure metals.
  • Shape memory alloys can be bent or deformed into a different shape
  • When heated they return to original shape
  • They can be used in many ways e.g dental braces.
  • When atoms are arranged into very small particles & behave differently to ordianry materials made of same atoms.
  • A nanometre is one billionth of a metre and nano particles are a few nanometres in size
  • Small sizes give very large surface areas & new prooperties that make them v. useful.
  • Nanotechnology uses nanoparticles as highly selective sensors, catalysts, coatings, cosmetics e.g sunscreen and deodorants, and to give construction materials special properties.
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Nanoscience (continued) & Properties of Polymers

  • As nanoparticles are used more,there is greater risk of them finding their way into the air and our bodies
  • This can have unpredictable consequences for our health & environment. it needs more research to find out effects.
  • Properties of a polymer depend on the monomer that makes it & condition made in.
  • Polypropene is made from proprene and softens at a higher temp than polyethene.
  • Low density polyethene and high density polyethene are made using different catalysts and different reaction conditions
  • HD polyethene has a higher softening temperature and is stronger than LD p(ethene)
  • Polyethene is a thermosoftening plymer. It's made of individual tangled polymer chains.
  • When heated, it's soft and when it cools it hardens again
  • This means it can be heated to mould into a shape and then heated and moulded again.
  • Other polymers named thermosetting polymers don't melt or soften when heated.
  • These polymers set hard when first moulded as covalent bonds form crosslinks between their polymer chains
  • The strong bonds hold the polymer chains in position.
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