Simple molecular structures
2 marks · HardState one property that distinguishes a simple molecular structure from a giant covalent structure. Explain how this property relates to the forces present in each structure.
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Also accept: Simple molecular structures have low melting and boiling points, while giant covalent structures have high melting and boiling points. This is because, in simple molecular substances, only weak intermolecular forces need to be overcome, but in giant covalent structures, strong covalent bonds must be broken.; Melting point is much lower in simple molecular compounds because their intermolecular forces are weak compared to the strong covalent bonds in giant structures.
Common mistakes: Omitting the difference in forces broken.; Confusing covalent bonds and intermolecular forces.
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Marking points
A1 · 1 mark · Identifies a property, e.g., simple molecular compounds have low melting/boiling points, giant covalent structures have high melting/boiling points.
A2 · 1 mark · Explains property in terms of the nature of forces present (weak intermolecular forces vs strong covalent bonds).
Worked solution
A simple molecular structure has low melting and boiling points, while a giant covalent structure has very high melting and boiling points. This is because only weak intermolecular forces are overcome in simple molecular compounds, but in giant covalent structures, strong covalent bonds throughout the structure must be broken.