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C4 Revision Notes
Polymers are long chains molecules formed when loads of small molecules called monomers
join together
This reaction is called polymerisation
In polymers all atoms are joined by strong covalent bonds
There are intermolecular forces between the chains
The intermolecular forces between the polymer molecules are strong, which means more
energy is needed to break them
This means that most polymers are solid at room temperature
Before polymers melt, they become soft
Low-density is made from ethene
There is a lot of space between the polymer chains so forces between the chains are weak
This means they are flexible and are used for bags and bottles
High-density is also made from ethene but under different conditions
The chains are packed more closely together, so the forces between them are strong,
this means it is stiff and is used for water tanks and drain pipes
As well as intermolecular forces between the chains some polymers also form covalent or ionic
crosslinks
Polymers that have intermolecular forces between the chains are made up of individual tangled
things that can slide over each other the forces between the chains can be overcome so the
polymers can be melted
In polymers that have crossed links between the chains as well as intermolecular forces the
chains are held very strongly these polymers don’t soften when heated
Their chains are hold together in a rigid structure making them strong, hard and stiff
Giant covalent structures contain many covalent bonds
Diamonds are sparkly and colorless
Each carbon atom forms four covalent bonds in a very rigid giant covalent structure which
means it's very hard
Diamond is usually used for cutting tools
Diamond has a very high melting point
It doesn't conduct electricity because it has no free electrons or ions
Graphite is black and opaque but still a little bit shiny
Each carbon atom only forms 3 covalent bonds, creating a sheet of carbon atoms which are free
to slide over each other new line the layers are held weekly so are slippery and can be rubbed
off onto paper to leave a black mark
This also makes graphite ideal as a lubricating material
Graphite has a high melting point
Due to there being a lot of free electrons that can move, this means that graphite can conduct
electricity
graphene is a single sheet of graphite
The carbon atoms are arranged in hexagons and each atom forms three covalent bonds

Melting point - at this temperature solid materials turn liquid full stop the stronger the forces
between particles the higher the melting point
Strength - strength is how good a material is at resisting a force
There are two types of strength
Tensile strength - how much a material can resist a pulling Force
Compressive strength - how much a material can resist a pushing Force
Stiffness - stiff materials don't bend when a force is applied
Hardness - the hardness of the material is how difficult it is to cut into
Brittleness - brittle materials break if they are hit by a sudden Force for example a hammer
Ease of reshaping - materials that deform but don't break when a force is applied to them can
be shaped
Conductivity - to conduct electricity, a material must have charged particles (ions or electrons)
which can move
Types of materials
Ceramics are stiff but brittle
Play is soft when it's wet, so it's easy to mould into different shapes
It is hardened by firing it at a very high temperature, it has high compressive strength
glass is transparent and strong, it can be molded when hot and can be brittle when thin
Most glass is Soda lime glass which is made by heating lime, sand and sodium carbonate until
they melt
Composites are made of different materials
Carbon fibre composites has been made using carbon atoms bonded together to make carbon
fibres or carbon nanotubes held together in a polymer resin Matrix
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This is sacrificial
protection
Polymers are really adaptable
...
They are much more brittle and stiff than other
materials but they are also strong and hard-wearing
Metals are good conductors of heat and electricity full stop they generally have high melting
points
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However metals corrode
easily
Composites have different properties depending on the binder and the reinforcement

Reusing means using the product again in the same form for example glass milk bottles
recycling means using the material in a product to make new things
life cycle assessment looks at each stage of the life of a product
Choice of materials - metals have to be mined and extracted from their ores
...
It
can also cause a lot of pollution
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000000001 m
Nanoparticles have a very high surface area to volume ratio
nanoparticles can modify the properties of materials
They have huge surface area to volume ratio so they can make good catalysts
Cosmetics such as sun creams have been made using nanoparticles
...

Nanoparticles are useful they might have risks that aren't fully understood
For example, if they are too small they can get deep into cells within the body

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