The physical properties of ionic substances
3 marks · NormalExplain why sodium chloride forms a giant ionic lattice instead of individual molecules. In your answer, refer to the charges on the ions and the overall structure.
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Because sodium chloride is made of oppositely charged ions (Na+ and Cl-), each ion attracts many ions of the opposite charge, causing them to arrange in a giant lattice rather than separate molecules. The forces of attraction act in all directions, so there are no distinct molecules, only a continuous lattice.
Also accept: Explanation that the charges cause each ion to be attracted to many surrounding ions, so molecules do not form.
Common mistakes: Referring to sodium chloride as a molecule; Not mentioning continuous three-dimensional structure
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Marking points
M1 · 1 mark · Mentions ionic bonding and opposite charges on Na+ and Cl- ions.
M2 · 1 mark · Explains that each ion is surrounded by several ions of opposite charge.
A1 · 1 mark · States there are no molecules, only a continuous three-dimensional giant ionic lattice.
Worked solution
Sodium chloride consists of Na+ and Cl- ions. Each sodium ion attracts several chloride ions, and each chloride ion attracts several sodium ions. These attractions occur in all directions, so the ions arrange themselves in a continuous, regular three-dimensional lattice. There are no separate molecules; instead, the ions are part of a giant ionic lattice.