What are they also,
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Also note that giant structure can be ionic or covalent.
The examples for giant covalent structure are graphite, diamond, other carbon allotropes, silicon dioxide (SiO2). You should google for pictures of these substances and you will see why they are called giant structure; many atoms are linked together to form a lattice (instead of 2, 3, 4,... atoms for simple molecules). Giant covalent structures usually have higher boiling, melting point due to their strong, extensive bonding.
These GCSE books are more clear than ours in IGCSE