Students should know that graphite is similar to metals in that it has…

The idea

Graphite is a giant covalent structure of carbon atoms arranged in hexagonal layers. Each carbon atom forms three covalent bonds, leaving one electron per atom delocalised within the layers. These delocalised electrons are free to move through the structure, so graphite conducts electricity and heat like a metal. Unlike metals, graphite is not malleable in the same way, because its layers are held by weak forces and can slide, and it has no sea of positive ions. A useful method is to compare graphite with a metal such as copper: both conduct because charged particles can move, but in copper the moving charges are electrons in a metallic lattice, while in graphite they are delocalised electrons within covalent layers. This explains why graphite is used for electrodes and feels slippery.

What earns the marks

• Graphite is a giant covalent structure in which each carbon atom is covalently bonded to three other carbon atoms.
• Each carbon atom contributes one electron that becomes delocalised, so delocalised electrons are present within the layers.
• The delocalised electrons are free to move, allowing graphite to conduct electricity and thermal energy.
• Graphite differs from metals because it has a layered covalent lattice rather than a lattice of positive ions.
• The weak forces between layers allow them to slide, which explains why graphite is slippery and useful as a lubricant.

Common mistakes and how to put them right

• Thinking graphite conducts because its ions move.

  Put it right by stating that the moving charges are delocalised electrons, not ions.

• Believing each carbon atom in graphite forms four covalent bonds.

  Put it right by noting that only three bonds form, leaving one delocalised electron per carbon atom.

• Confusing graphite with diamond and saying it does not conduct.

  Put it right by explaining that diamond has no delocalised electrons, whereas graphite does.

Exam tips

• Link the structure of graphite directly to its property of conduction in one sentence, for example: three bonds per carbon atom leave delocalised electrons that can move.
• When comparing graphite with metals, name the similarity (delocalised electrons) and one difference (layered covalent structure versus positive ion lattice).
• Use the phrase delocalised electrons rather than free electrons if the question asks for the reason graphite conducts, and avoid saying electrons are shared between layers.