Chemistry · Structure and bonding of carbon
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A manufacturer is choosing carbon materials for different products. Diamond is being considered for a cutting tool, graphite for a pencil, and graphene for a lightweight electrical composite. Explain how the structures and bonding of these forms of carbon make them suitable for these uses, and describe how the structure of carbon nanotubes gives them a different useful property.
Level 3 (5-6): Relevant points (reasons/causes) are identified, given in detail and logically linked to form a clear account. Level 2 (3-4): Relevant points (reasons/causes) are identified, and there are attempts at logically linking. The resulting account is not fully clear. Level 1 (1-2): Points are identified and stated simply, but their relevance is not clear and there is no attempt at logical linking. No relevant content (0).
Diamond would be good for a cutting tool because it is very hard. Graphite is used in pencils because it is soft and leaves a mark. Graphene is thin and nanotubes are strong, so they could be useful materials.
What this answer missed
- •diamond has a rigid three-dimensional network of strong covalent bonds, which makes it very hard
- •graphite has layers with weak forces between them, so the layers slide over each other and graphite is soft enough to leave a mark
- •graphene is a single layer of graphite, one atom thick, so it has low mass while remaining strong for a lightweight composite
- •graphene has delocalised electrons that can move through the layer, so it conducts electricity for an electrical composite
- •carbon nanotubes are cylindrical fullerenes with a very high length-to-diameter ratio, so they can reinforce materials
Diamond has strong bonds so it does not wear away easily when cutting. Graphite is made in layers which can come off onto the paper, so it works in pencils. Graphene is very thin, and carbon nanotubes are long and strong.
What this answer missed
- •Diamond has a rigid three-dimensional network of strong covalent bonds, which makes it extremely hard.
- •Graphite has weak forces between its layers, so the layers can slide off onto the paper.
- •Graphene is one layer of carbon atoms, so it has very low mass while remaining strong, making it suitable for a lightweight composite.
- •Graphene has delocalised electrons that can move through the layer, so it conducts electricity well.
- •Carbon nanotubes are cylindrical carbon structures with a very high length-to-diameter ratio, so they can reinforce materials.
Diamond has a three-dimensional network of carbon atoms, with each atom joined to four others by strong covalent bonds. This makes it very hard, so it is suitable for a cutting tool. Graphite has layers of carbon atoms, and the layers can slide over each other, making it soft and useful in pencils. Graphene is one layer of graphite, so it has very little mass but is still strong, making it useful in a lightweight composite.
What this answer missed
- •Carbon nanotubes are cylindrical fullerenes with a very high length-to-diameter ratio, so they can reinforce materials and be used to strengthen products such as tennis rackets.
Diamond has each carbon atom covalently bonded to four other carbon atoms in a rigid giant structure. The strong bonds make it very hard, so it can be used for cutting. Graphite has layers in which each carbon atom is bonded to three others. There are weak forces between the layers, allowing them to slide, so graphite is soft and useful in pencils. Its delocalised electrons can also move, so it conducts electricity. Graphene is a single layer of graphite, so it is very light but strong, and its delocalised electrons allow it to conduct electricity in a composite. Carbon nanotubes are cylindrical structures with a very large length compared with their diameter, so they are strong and can reinforce materials.
- •Diamond has a rigid giant covalent structure in which each carbon atom is covalently bonded to four other carbon atoms.
- •The strong bonds in diamond make it very hard, so it is suitable for cutting.
- •Graphite has layers in which each carbon atom is bonded to three other carbon atoms.
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