Giant covalent structures
Covalent bonding between carbon atoms can be extended to form giant structures. What are they like?
Diamond
Diamond is a giant covalent structure made
from carbon atoms. Each atom is bonded to
four neighbours. The pattern is repeated
billions of times.
The covalent bonds between neighbouring
carbon atoms are very strong.
This means that:
 Diamond has a very high melting point
because its covalent bonds are so strong
 Diamond is very hard because the atoms are
so strongly bonded together in all directions.
Diamond is the hardest natural material
Graphite
Graphite is a giant
covalent layered
structure made from
carbon atoms.
Each layer contains carbon
atoms bonded to
three neighbours, leaving
one of its outer shell
electrons ‘delocalised’ and ‘free’ to roam between the layers, similar to metals, but
they operate between the layers.
Graphite is therefore an electrical conductor, unlike diamond which uses all four of
its outer shell electrons to form covalent bonds so has no ‘free’ electrons.
The layers are weakly bonded and can slide over each other. Graphite is very soft
and makes an excellent lubricant for moving parts (e.g. motor bike chains … )
The carbon atoms within the layer are strongly bonded together just as in diamond.
Graphite therefore has a high melting point.
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Nanomaterials
Nanoparticles are made from just a few hundred atoms. They measure between 1
and 100 nanometres across. They are very new to us and incredibly useful.
Fullerenes are carbon structures based upon
hexagonal rings of carbon as in the layers of
graphite.
Buckminsterfullerene is a molecule of pure carbon
with sixty atoms arranged as a hollow sphere (a
buckyball) C60. Fullerenes can be used to cage
radioactive metal atoms or drug molecules and
help deliver them to cancer cells.
Nanotubes are fullerenes with huge
surface areas compared to their
volumes. Therefore they make excellent
catalysts.
Nanotubes are used to stiffen graphite
tennis racquets.
Nanoparticles have different properties from the same
substance in their normal sized pieces.
Titanium dioxide powder is a white solid used to make
house paint. The white powder reflects all colours in
sunlight so the paint appears white!!
If we use titanium dioxide nanoparticles in sun cream, the
tiny nanoparticles are too small to reflect sunlight. You
cannot see them! They make excellent sun block creams
protecting your skin from harmful UV light, making your
skin look white.
Other uses include:
 self-cleaning coatings in ovens;
 building materials that are strong and light;
 better computer chips;
 self-cleaning window glass coating
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Polymers as structures
Polymers are long chains of carbon atoms with hydrogen and or other groups attached to them.
The attached atoms and the conditions used to manufacture the polymer determines the
structure of the polymer and its physical characteristics (and behaviour).
LDPE or low density
poly(ethene) is used to
make plastic bags.
Poly(ethene)
HDPE or high density
poly(ethene) is used to
make plastic bottles
 density = 0.92g/cm3
 density = 0.95g/cm3
 low tensile strength
 high tensile strength
 transparent
 transparent
 it is very flexible
 it is stiff
 Manufacturing conditions
a) 300 ℃
b) 1 atmosphere pressure
c) aluminium oxide
catalyst
Manufacturing conditions:
a) 100-300 ℃
b) 1500-3000 atmospheres
c) oxygen/peroxide
catalyst
Thermosets and thermoplastics
Some polymers melt when heated and change their shape when they cool, others char but
don't drip when heated. The behaviour of polymers is linked to their inner structures.
Thermo-setting plastics
These polymers consist of:
 long polymer chains
 cross-links between polymer molecules
 thermosets cannot be reshaped because they don’t melt when heated
 thermosets are hard to melt because they have strong bonds holding the
molecule chains together
 they are hard and have a rigid shape
Thermo-softening polymers
These polymers consist of:
 long tangled polymer chains
 they can be recycled because they
can be re-shaped easily
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