AQA · GCSE · Chemistry
Course version: 8462 · Version from Sept 2018
The covalent bonds in molecules and giant structures can be represented in…
Full specification wording
Covalent bonding: The covalent bonds in molecules and giant structures can be represented in the following forms: Polymers can be represented in the form: where n is a large number.
Covalent bonds can be shown in several ways.
Checked against the AQA 8462 specification (opens in a new tab) on .
- Point 7 of 8
- 4 key terms
Study notes
From the checked teaching notes for this specification point.
The idea
Covalent bonds can be shown in several ways. A dot and cross diagram shows the outer-shell electrons of each atom, with shared pairs in the overlap. A line between two atoms represents a single covalent bond, and a double line represents a double bond. Ball and stick models show the three-dimensional shape, while displayed formulae show every atom and bond in two dimensions. Polymers are represented by drawing the repeating unit inside brackets with the letter n outside, where n is a large number of repeating units. For example, poly(ethene) is shown as the ethene repeating unit in brackets with n outside. The value of n is not a fixed number; it simply shows that many units are joined together.
What earns the marks
- A dot and cross diagram shows outer-shell electrons, with shared pairs in the overlap between atoms.
- A single line between two atoms represents one shared pair of electrons, and a double line represents two shared pairs.
- Ball and stick models show the arrangement of atoms in three dimensions but do not show electron pairs.
- A polymer is represented by placing the repeating unit in brackets with n outside, where n is a large number.
- The repeating unit must show the correct atoms and bonds, with bonds extending beyond the brackets to show the chain continues.
Common mistakes and how to put them right
Drawing a polymer repeating unit without brackets or without n.
Put it right by enclosing the repeating unit in brackets and writing n outside.
Showing a double bond inside a polymer repeating unit.
Put it right by drawing single bonds only, because the double bond opens during polymerisation.
Treating n as a small fixed number such as 2 or 3.
Put it right by stating that n is a large number of repeating units.
Exam tips
- When drawing a polymer, check that the bonds at each end of the repeating unit pass through the brackets.
- Use a line for each single bond and two parallel lines for a double bond, and keep the number of lines consistent with the atoms shown.
- If asked what n represents, state that it is a large number of repeating units, not a specific value.
Try the lesson
The start of the Covalent bonding: The covalent bonds in molecules and giant structures can be represented in the following forms: Polymers can be represented in the form: where n is a large number. lesson, made from checked teaching notes for this specification point.
Have a go first
In the displayed formula of a polymer, what does the symbol n represent?
Listen
Covalent bonds can be shown in several ways. A dot and cross diagram shows the outer-shell electrons of each atom, with shared pairs in the overlap. A line between two atoms represents a single covalent bond, and a double line represents a double bond. Ball and stick models show the three-dimensional shape, while displayed formulae show every atom and bond in two dimensions. Polymers are represented by drawing the repeating unit inside brackets with the letter n outside, where n is a large number of repeating units. For example, poly(ethene) is shown as the ethene repeating unit in brackets with n outside. The value of n is not a fixed number; it simply shows that many units are joined together. A strong answer earns marks for these points. A dot and cross diagram shows outer-shell electrons, with shared pairs in the overlap between atoms. A single line between two atoms represents one shared pair of electrons, and a double line represents two shared pairs. Ball and stick models show the arrangement of atoms in three dimensions but do not show electron pairs. A polymer is represented by placing the repeating unit in brackets with n outside, where n is a large number. A common slip: Drawing a polymer repeating unit without brackets or without n. Instead, enclosing the repeating unit in brackets and writing n outside. Exam tip: When drawing a polymer, check that the bonds at each end of the repeating unit pass through the brackets.
See it
Key words
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Dot and cross diagrams
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Polymer notation
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Repeating units
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n
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See every definition
- Dot and cross diagrams
- A representation that shows the outer-shell electrons of each atom, with shared pairs in the overlap between atoms.
- Polymer notation
- A representation in which the repeating unit is placed in brackets with n outside, where n is a large number.
- Repeating units
- The unit placed in brackets with n outside, showing the correct atoms and bonds, with bonds extending beyond the brackets to show the chain continues.
- n
- A large number of repeating units, not a specific value.
Label the diagram
Some boxes have lost their names. Pick the right name for each number.
1Box 1
2Box 2
3Box 3
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