Chemistry Unit 2- Structure and Properties

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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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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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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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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