MYP 9 Unit 3

Structure and bonding: 9.3.8: Giant covalent substances


  • To know that covalent bonding can extend over the whole structure in certain substances (sand, graphite, diamond)
  • To know the general properties of giant covalent elements and compounds
  • To draw a section of diamond and graphite
  • To understand how the arrangement of atoms in the giant structure influences property


Build molymods of diamond and graphite in groups

Discuss properties of allotropes.

Point out that many elements have allotropic forms (eg oxygen and ozone)

Student follow up

Research diamond and graphite properties

Include graphene and fullerenes

Teacher's notes

Silicon dioxide should also be covered


Videos on allotropes, graphene and fullerene

The allotropes of carbon

The allotropes of carbon

The allotropes of carbon

Silicon dioxide

Giant covalent structures



C2.2.3 Covalent structures

a) Atoms that share electrons can also form giant structures or macromolecules. Diamond and graphite (forms of carbon) and silicon dioxide (silica) are examples of giant covalent structures (lattices) of atoms. All the atoms in these structures are linked to other atoms by strong covalent bonds and so they have very high melting points.

Candidates should be able to recognise other giant structures or macromolecules from diagrams showing their bonding

b) In diamond, each carbon atom forms four covalent bonds with other carbon atoms in a giant covalent structure, so diamond is very hard.

c) In graphite, each carbon atom bonds to three others, forming layers. The layers are free to slide over each other because there are no covalent bonds between the layers and so graphite is soft and slippery.

Higher Tier candidates should be able to explain the properties of graphite in terms of weak intermolecular forces between the layers.

d) In graphite, one electron from each carbon atom is delocalised. These delocalised electrons allow graphite to conduct heat and electricity.

Candidates should realise that graphite is similar to metals in that it has delocalised electrons.

e) Carbon can also form fullerenes with different numbers of carbon atoms. Fullerenes can be used for drug delivery into the body, in lubricants, as catalysts, and in nanotubes for reinforcing materials, eg in tennis rackets.

Candidates' knowledge is limited to the fact that the structure of fullerenes is based on hexagonal rings of carbon atoms

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IsisSoft 2014