An introduction to graphite and diamond which are allotropes of carbon.
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Table of content
Introduction .........................................................3
Properties of graphite and diamond ....................4
Structure of graphite and diamond ......................5
Structure of graphite ............................................6
Structure of diamond ...........................................7
Structure and bonding affects properties ............8
References ..........................................................9
Introduction
Graphite and diamond are allotropes of carbon. Both graphite and diamond have a giant molecular structure which consists of a lattice of carbon atoms held together by strong covalent bonds.
Click on this link to see a map of different chemical structures.
Properties of Graphite and Diamond
Both graphite and diamond have very high melting points and are insoluble in all solvents.
They have different hardness. Graphite is soft and has lubricating properties. Graphite can be found in your pencil, as you write the soft graphite breaks off and is transferred to the paper. Diamond is the hardest natural substance known and is often used as an abrasive or in cutting tools.
Graphite is a good conductor of electricity while diamond does not conduct electricity.
Structure of Graphite and Diamond
The structure of a material refers to the way the particles are arranged. In graphite and diamond, the particles are carbon atoms which are represented by black spheres in the diagram above. The black lines represent the covalent bonds between carbon atoms.
Structure of Graphite
Graphite is made up of layers of carbon atoms arranged hexagonally. Within the layer, each carbon atom is covalently bonded to three other carbon atoms. The fourth valence electron is delocalised throughout the layer. The bonds between the layers are weak van der Waals forces of attraction.
Click on this link to build the graphite structure.
Structure of Diamond
Diamond consists of a three dimensional network of carbon atoms. Each carbon atom is covalently bonded to four other carbon atoms in a tetrahedral arrangement.
Click on this link to build the diamond structure.
Structure and bonding affects property
Let's consider how the structure and bonding in two allotropes of carbon affects their physical properties.
Melting point - large amounts of energy is required to break the strong carbon-carbon bonds in graphite and diamond.
Solubility - solvent molecules are unable to penetrate the graphite and diamond lattice because of the strong covalent bonds between carbon atoms. Thus they are both insoluble in all solvents.
Hardness - Graphite is soft and has lubricative properties because of the relatively weak van der Waals forces between layers. This allows the layers to slide over each other. Diamond is very hard because of its rigid tetrahedral arrangement of atoms held by strong carbon-carbon bonds, giving it a strong and rigid structure.
Electrical conductor - Graphite conducts electricity as it has delocalised electrons between the layers. Diamond has no mobile electrons to conduct electricity as all the 4 valence electrons of each carbon atom are involved in covalent bonds.
References
- Avogadro Website - Chemical Structures
- Wikipedia - Diamond and graphite
- GCSE Bitesize - Different substances and their properties