4.1.1Guiding Spaceship Earth Towards a Sustainable Future
Bonding and Structure In Forms Of Carbon — AQA GCSE Combined Science Synergy 8465 - Physical Sciences Revision Notes & Topical Questions
5 min read 6 parts Lesson 2 of 15
Section 1 of 6Allotropes of carbon
Same element, different structures
- Same element, different structures Allotropes are different structural forms of the same element in the same physical state.
- Diamond, graphite, graphene and fullerenes are all made only of carbon atoms.
Structure controls properties
- Structure controls properties Differences in how the atoms are joined explain the large differences in hardness and electrical conductivity.
Section 2 of 6Diamond and graphite
| Feature | Diamond | Graphite |
|---|---|---|
| Bonds per carbon atom | Four covalent bonds | Three covalent bonds |
| Arrangement | Rigid 3D lattice of tetrahedra | Flat layers of hexagons |
| Hardness | Very hard | Soft and slippery, layers slide over each other |
| Melting point | Very high, many strong bonds to break | Very high, strong bonds within the layers |
| Electrical conductivity | None, no free electrons | Good, delocalised electrons move along the layers |
| Uses | Cutting tools, drill tips, jewellery | Electrodes, lubricant, pencils |
Section 3 of 6Why graphite conducts
1Three bonds only
- Three bonds only Each carbon uses three of its four outer electrons in bonding.
2One electron left over
- One electron left over The fourth electron on each atom is not in a bond.
3Delocalised electrons
- Delocalised electrons These electrons are free to move between and along the layers.
4Charge carried
- Charge carried The moving electrons carry a current, so graphite conducts.
Section 4 of 6Graphene and fullerenes
Other carbon forms
Graphene
- Graphene A single layer of graphite, one atom thick. It is very strong, light and an excellent conductor.
Buckminsterfullerene
- Buckminsterfullerene C60, a hollow sphere of carbon atoms in hexagons and pentagons.
Nanotubes
- Nanotubes Rolled-up sheets of graphene forming tiny cylinders with a high length-to-diameter ratio.
- They are strong and conduct electricity, and are used in nanotechnology and to strengthen materials.
Fullerene uses
- Fullerene uses Delivering drugs in the body, lubricants and catalyst supports.
Section 5 of 6Key terms
| Term | Meaning |
|---|---|
| Allotrope | One of two or more different forms of the same element in the same physical state. |
| Giant covalent structure | A huge network of atoms joined by strong covalent bonds. |
| Delocalised electron | An electron that is not attached to one atom and can move through the structure. |
| Graphene | A single layer of graphite, one atom thick. |
| Nanotube | A cylinder of carbon atoms with a diameter of a few nanometres. |
Section 6 of 6Exam technique
1
Explaining that graphite is soft because its covalent bonds are weak. The bonds are strong; the forces between the layers are weak.
2
Saying diamond conducts because it has covalent bonds. It has no free electrons.
3
Forgetting that graphite has a high melting point even though it is soft.
4
Calling carbon dioxide or methane giant covalent structures; those are small molecules.
5
Describing delocalised electrons as ions.
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