Diamonds are Forever!
L.O: To understand the properties of giant
covalent structures
Why is diamond so hard?
Why can you melt diamond?
If diamond is covalent why isn’t it a liquid or gas?
Why isn’t graphite called carbon when it is actually just
carbon?
Why does graphite conduct?
Make a carbon molecule? Can you turn it into a
macromolecule.
C
C
C
C
C
Giant covalent structures
This is diamond what sort of properties do you think it will
have?
In some substances, millions of atoms join together by
covalent bonding. This produces giant covalent
structures, (macromolecules) – a 3D structure not
molecules.
Cut out each of the diagrams and work out which are:
Diamond (Lots of atoms joined)
Graphite (forms layers)
Silicon dioxide (SiO2)
Buckminsterfullerene (ball structure)
You should have a diagram of a molecule and giant
structure for each. List some properties that you
think each macromolecule will have
The structure of diamond
Diamond is a rare form of carbon
in which each atom is covalently
bonded to four others. This
pattern arrangement is repeated
millions of times to create a giant
lattice.
C
C
C
C
C
Properties: Hard, very high
melting and boiling point, shiny
and transparent, unreactive
The structure of graphite
Graphite is a much more
common form of carbon. in
which each atom is covalently
bonded to three others, leaving
one free bond.
This forms rings of six atoms,
creating a giant structure
containing many layers. These
layers are held together by
weak forces of attraction.
C
C
C
C
weak forces of attraction
Properties of graphite




free electrons (also called delocalised electrons)
These allow it to conduct electricity ( as a flow of
electrons = electric current)
layers slide over each other easily
Uses: in pencils (the hardness is altered by changing
the clay and graphite ratio)
Why is graphite sometimes used as a lubricant?
Other allotropes of carbon
Other allotropes of carbon have been discovered in the last 30 years. They
are large but not really giant structures.
One allotrope is buckminsterfullerene. It contains 60 carbon atoms, each of
which bonds with three others by forming two single bonds and one double
bond.
These atoms are arranged in 12 pentagons and 20 hexagons to form spheres,
which are sometimes called ‘bucky balls’.
Hard, high melting and boiling point
C
C
C
C
Sand
Sand is an impure form of silicon dioxide (quartz). It has a
giant covalent structure with certain similarities to diamond.
Each silicon atom (2.8.4) is bonded to four
oxygen atoms, and each oxygen atom (2.6)
is bonded to two silicon atoms.
O
O
Si
O
O
Effect of structure on properties
Giant Covalent properties
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

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Giant covalent structures have high melting points
Many are very hard
Most do not conduct electricity or dissolve in water
They are chemically unreactive