Giant covalent structures
• What do these images have in common?
• How are they different?
• What do you know about the uses of graphite
and carbon?
Learning questions
• What are giant covalent molecules?
• How are they similar/ different from each other?
• Why do they have different properties to simple
covalent molecules?
• What is meant by allotropes of carbon?
Which of the molecules do you think will be
more difficult to separate? Why? Which will
have the highest melting point?
Simple covalent molecule
Eg. hydrogen
Giant covalent
molecule
What are giant covalent structures?
In some substances, such as sand, diamond and graphite,
millions of atoms are joined together by covalent bonds.
The covalent bonds in these substances do not form
molecules but vast networks of atoms called giant
covalent structures.
All the bonds are covalent, so giant covalent structures have
very high melting and boiling points, and are usually hard.
What are the allotropes of carbon?
Diamond and graphite appear to be very different substances but
what do they have in common?
Both diamond and graphite are made up of carbon atoms.
Different forms of the same element are called allotropes.
These allotropes of carbon have different properties because the
atoms are bonded in different arrangements which create different
giant structures.
Remember each dot represents a carbon element.
Diamond
Graphite
Buckminster
-fullerene
• Decide on the key features of each structure, so you
would recognise it again.
• Why do you think carbon can make so many different
structures?
What are the differences between
these two materials?
Diamond
Graphite
We will now consider...
• Why are they different?
• Why is this useful to know?
Research task
Using the textbooks and the images provided complete these
tasks in your book:
1. Explain what the allotropes of carbon are and what the term
means.
2. Explain why these are known as giant covalent structures.
3. Describe the bonding and structure of diamond and graphite
and explain the differences.
4. State the properties of diamond and carbon (melting point,
electrical conductivity etc)
Extension:
Explain how the structure cause the properties of diamond and
graphite.
Properties of diamond
• Each carbon has 4
strong covalent bonds.
• How will this affect its
melting point? Why?
• All electrons are used in
the bonds.
• Should it be able to
conduct electricity?
Why?
Diamond
Properties of graphite
Graphite
• Each carbon has 3 strong
covalent bonds.
• How will this affect its
melting point? Why?
• 1 free (delocalised)
electron from each
carbon.
• Should it be able to
conduct electricity? Why?
• Layers with weak forces
holding them together.
• What will this cause?
Explaining properties of allotropes
Use the information you have discovered about the allotropes of
carbon to answer the following questions.
1. Why is diamond used in cutting tools? Explain the important
properties.(4)
2. What properties of diamond make it good for jewellery? (2)
3. Why is graphite used in pencils? (2)
4. What makes graphite useful as an electrode in electrolysis? Explain
these properties.(4)
5. What property of graphite makes it good as a lubricant? Explain
why this property exists. (3)
Are there other allotropes of carbon?
A third class of carbon compounds have been discovered in
recent years. These are called fullerenes.
Buckminsterfullerene is one type of fullerene. It contains 60
carbon atoms, each of which is bonded to three others by two
single bonds and one double bond.
C
C
C
C
The atoms in this allotrope of carbon form a sphere, like the shape
of a football. The molecules can be called ‘bucky balls’.
They are large but are not classified as giant structures.
Plenary
• Write down one thing you knew before the
lesson and 2 things you have learnt in the
lesson.