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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