DiamondOxford AQA IGCSE Chemistry: Revision notes
Section 1
What is diamond?
Diamond is one of the forms (allotropes) of the element carbon. It is a giant covalent structure in which each carbon atom forms four covalent bonds with four other carbon atoms, building a rigid three-dimensional lattice that extends throughout the whole crystal.
Section 2
Why is diamond so hard?
Diamond's hardness comes directly from its bonding:
- Every carbon atom is joined to four neighbours by strong covalent bonds
- These bonds point in every direction through the structure, forming a rigid 3D network
- Because there are no weak points and every bond is a strong covalent bond, a huge amount of energy is needed to break the structure apart
This makes diamond the hardest naturally occurring substance.
Always explain hardness in terms of the four strong covalent bonds per atom, not just 'strong bonds' — examiners want the number four and the word 'covalent'.
Section 3
Does diamond conduct electricity?
Diamond does not conduct electricity. Unlike graphite, every one of carbon's four outer-shell electrons is used in a covalent bond, so there are no delocalised (free) electrons available to carry a charge through the structure.
A common error is saying diamond 'has no electrons' — it has plenty, they are just all locked into covalent bonds rather than free to move.
Must Know
- Diamond is a giant covalent structure made entirely of carbon atoms
- Each carbon atom forms four covalent bonds to four other carbon atoms
- Diamond is very hard because of its rigid 3D lattice of strong covalent bonds
- Diamond has a very high melting point because many strong covalent bonds must be broken
- Diamond does not conduct electricity — all outer electrons are held in covalent bonds, none are delocalised
That's the notes covered.
Carry on to the next subtopic.