AQA · GCSE · Chemistry
Course version: 8462 · Version from Sept 2018
Students should be able to recognise giant covalent structures from…
Full specification wording
Giant covalent structures: Students should be able to recognise giant covalent structures from diagrams showing their bonding and structure.
Recognising a giant covalent structure from a diagram means identifying a continuous network of atoms joined by covalent bonds, with no separate molecules and no finite repeating unit.
Checked against the AQA 8462 specification (opens in a new tab) on .
- Point 5 of 5
Study notes
From the checked teaching notes for this specification point.
The idea
Recognising a giant covalent structure from a diagram means identifying a continuous network of atoms joined by covalent bonds, with no separate molecules and no finite repeating unit. In a diagram of diamond, each carbon atom is shown with four bonds extending in three dimensions to other carbon atoms. In graphite, each carbon atom is shown with three bonds within a flat hexagonal layer, and the layers are stacked with delocalised electrons between them. In silicon dioxide, silicon and oxygen atoms alternate in a continuous network, with each silicon atom bonded to four oxygen atoms and each oxygen atom bonded to two silicon atoms. A diagram of a simple molecular substance, by contrast, shows small groups of atoms with weak forces between the groups.
What earns the marks
- A giant covalent diagram shows a continuous network of atoms joined by covalent bonds extending in two or three dimensions.
- There are no separate small molecules in the diagram; every atom is bonded into the network.
- In a diamond diagram, each carbon atom is shown with four single covalent bonds in a tetrahedral arrangement.
- In a graphite diagram, each carbon atom is shown with three covalent bonds in hexagonal layers, with delocalised electrons between layers.
- In a silicon dioxide diagram, each silicon atom is bonded to four oxygen atoms and each oxygen atom is bonded to two silicon atoms.
- A diagram of a simple molecular substance can be distinguished because it shows small discrete groups of atoms rather than a continuous network.
Common mistakes and how to put them right
Mistaking a diagram of a simple molecular substance for a giant covalent structure because both show covalent bonds.
Put it right by checking whether the diagram shows a continuous network or small separate groups of atoms.
Assuming that any diagram with many atoms is giant covalent.
Put it right by looking for a repeating continuous network rather than many separate molecules.
Failing to notice the number of bonds around each atom in a diagram.
Put it right by counting the bonds, for example four around each carbon atom in diamond and three around each carbon atom in graphite.
Exam tips
- Count the bonds around a labelled atom in the diagram and use that number to identify the substance or its arrangement.
- Look for a continuous network with no separate molecules as the key feature of a giant covalent structure.
- If the diagram shows layers, check whether there are delocalised electrons between them, which indicates graphite.
Try the lesson
The start of the Giant covalent structures: Students should be able to recognise giant covalent structures from diagrams showing their bonding and structure. lesson, made from checked teaching notes for this specification point.
Have a go first
When examining diagrams of different substances, which visual feature indicates that a substance has a giant covalent structure?
Listen
Recognising a giant covalent structure from a diagram means identifying a continuous network of atoms joined by covalent bonds, with no separate molecules and no finite repeating unit. In a diagram of diamond, each carbon atom is shown with four bonds extending in three dimensions to other carbon atoms. In graphite, each carbon atom is shown with three bonds within a flat hexagonal layer, and the layers are stacked with delocalised electrons between them. In silicon dioxide, silicon and oxygen atoms alternate in a continuous network, with each silicon atom bonded to four oxygen atoms and each oxygen atom bonded to two silicon atoms. A diagram of a simple molecular substance, by contrast, shows small groups of atoms with weak forces between the groups. A strong answer earns marks for these points. A giant covalent diagram shows a continuous network of atoms joined by covalent bonds extending in two or three dimensions. There are no separate small molecules in the diagram; every atom is bonded into the network. In a diamond diagram, each carbon atom is shown with four single covalent bonds in a tetrahedral arrangement. In a graphite diagram, each carbon atom is shown with three covalent bonds in hexagonal layers, with delocalised electrons between layers. A common slip: Mistaking a diagram of a simple molecular substance for a giant covalent structure because both show covalent bonds. Instead, checking whether the diagram shows a continuous network or small separate groups of atoms. Exam tip: Count the bonds around a labelled atom in the diagram and use that number to identify the substance or its arrangement.
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