AQA · GCSE · Chemistry
Course version: 8462 · Version from Sept 2018
The structure of sodium chloride can be represented in the following forms:
Full specification wording
Ionic compounds: The structure of sodium chloride can be represented in the following forms:
Sodium chloride has a giant ionic lattice that can be represented in several ways.
Checked against the AQA 8462 specification (opens in a new tab) on .
- Point 4 of 6
Study notes
From the checked teaching notes for this specification point.
The idea
Sodium chloride has a giant ionic lattice that can be represented in several ways. A dot and cross diagram shows the transfer of electrons from sodium to chlorine, forming Na⁺ and Cl⁻ ions, but it usually shows only one formula unit. A ball and stick model uses spheres for ions and sticks for bonds, making the three-dimensional arrangement clear but implying that ions are joined by directional bonds. A two-dimensional diagram shows a flat cross-section of the lattice, which is easy to draw but does not show the full three-dimensional arrangement. A three-dimensional model shows the true arrangement of ions in space, with each Na⁺ surrounded by six Cl⁻ ions and vice versa. Each representation has limitations, so chemists choose the one that best communicates the feature they want to show.
What earns the marks
- Dot and cross diagrams show electron transfer and the resulting ions, but often only for one formula unit.
- Ball and stick models show the three-dimensional arrangement but can imply that ions are joined by directional covalent bonds.
- Two-dimensional diagrams are simple to draw but do not show the full three-dimensional lattice.
- Three-dimensional models show the true spatial arrangement of ions in the lattice.
- Each representation has limitations, so the choice depends on what feature is being emphasised.
Common mistakes and how to put them right
Thinking that a dot and cross diagram shows the whole lattice.
Put it right by stating it usually shows only one formula unit.
Believing that sticks in a ball and stick model represent covalent bonds.
Put it right by explaining they are just a way to show the arrangement of ions.
Assuming a two-dimensional diagram shows the full three-dimensional structure.
Put it right by stating it is a flat cross-section.
Exam tips
- When asked about limitations, state what the representation shows well and what it fails to show.
- Use the correct terminology: dot and cross, ball and stick, two-dimensional, three-dimensional.
- Link the representation to the feature it best illustrates, such as electron transfer or spatial arrangement.
Try the lesson
The start of the Ionic compounds: The structure of sodium chloride can be represented in the following forms: lesson, made from checked teaching notes for this specification point.
Have a go first
Which representation of sodium chloride uses spheres connected by lines or rods to illustrate the arrangement of ions?
Listen
Sodium chloride has a giant ionic lattice that can be represented in several ways. A dot and cross diagram shows the transfer of electrons from sodium to chlorine, forming Na⁺ and Cl⁻ ions, but it usually shows only one formula unit. A ball and stick model uses spheres for ions and sticks for bonds, making the three-dimensional arrangement clear but implying that ions are joined by directional bonds. A two-dimensional diagram shows a flat cross-section of the lattice, which is easy to draw but does not show the full three-dimensional arrangement. A three-dimensional model shows the true arrangement of ions in space, with each Na⁺ surrounded by six Cl⁻ ions and vice versa. Each representation has limitations, so chemists choose the one that best communicates the feature they want to show. A strong answer earns marks for these points. Dot and cross diagrams show electron transfer and the resulting ions, but often only for one formula unit. Ball and stick models show the three-dimensional arrangement but can imply that ions are joined by directional covalent bonds. Two-dimensional diagrams are simple to draw but do not show the full three-dimensional lattice. Three-dimensional models show the true spatial arrangement of ions in the lattice. A common slip: Thinking that a dot and cross diagram shows the whole lattice. Instead, stating it usually shows only one formula unit. Exam tip: When asked about limitations, state what the representation shows well and what it fails to show.
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