iGCSE Chemistry (0620) Core:2.6 Giant covalent structures: Exam Style Questions Paper 1- New Syllabus
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Detailed solution:
In graphite, each carbon atom is bonded to only three others (not four), forming hexagonal layers. Statement 1 is wrong. Graphite conducts electricity because it has delocalised electrons between the layers, not because it contains free ions. So statement 2 is also wrong. However, the layers are held together by weak forces and can easily slide over each other, making graphite a great lubricant. Only statement 3 is correct.
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Detailed solution:
A giant covalent structure is a huge network of atoms all connected by covalent bonds. Sodium chloride and magnesium chloride are ionic compounds with giant ionic lattices, not covalent networks. Ammonia is a simple molecular substance made of small $NH_3$ molecules with weak intermolecular forces. Graphite is a perfect example of a giant covalent structure, where each carbon atom is covalently bonded to three others, forming layers of interlocking hexagons that extend throughout the whole solid.
▶️ Answer/Explanation
Detailed solution:
Diamond is an allotrope of carbon where each carbon atom is covalently bonded to four other carbon atoms, forming a continuous three-dimensional giant lattice structure. This makes it extremely hard with a very high melting point. Ammonia (NH₃), carbon dioxide (CO₂), and water (H₂O) are all simple molecular compounds made of small molecules held together by weak intermolecular forces, not giant covalent structures.