This topic summary covers Knowledge Organiser: Giant Covalent Structures within Giant Covalent Structures for GCSE Chemistry. Revise Giant Covalent Structures in Bonding & Structure for GCSE Chemistry with 21 exam-style questions and 21 flashcards. This topic appears regularly enough that it should still be part of a steady revision cycle. It is section 12 of 12 in this topic. Use this topic summary to connect the idea to the wider topic before moving on to questions and flashcards.
Knowledge Organiser: Giant Covalent Structures
Key Terms
- Giant covalent: atoms bonded in all directions — no molecules
- Allotrope: different structural form of same element
- Delocalised electron: free electron that enables conduction
- Fullerene: hollow carbon cage (C₆₀) — simple molecular
- Graphene: single layer of graphite
Must-Know Facts
- Diamond: 4 bonds per C, very hard, no conduction, transparent
- Graphite: 3 bonds per C, soft layers, conducts (free e⁻), black
- SiO₂: similar to diamond, hard, high MP, no conduction
- All giant covalent structures have very high melting points
- Graphite conducts because 1 free electron per C atom
- Graphite is soft because layers slide (weak intermolecular forces between layers)
Key Equations
- Diamond: each C bonded to 4 others in tetrahedral arrangement
- Graphite: each C bonded to 3 others; 1 delocalised electron per C
- SiO₂: each Si bonded to 4 O atoms; each O bridges 2 Si atoms
- C₆₀ (buckminsterfullerene): 60 C atoms, 20 hexagons + 12 pentagons
Common Mistakes
- Saying diamond conducts electricity: Diamond has no free electrons — all 4 outer electrons are used in covalent bonds
- Saying graphite has a high melting point because of ionic bonds: Graphite is giant covalent — high MP is due to many strong covalent bonds within layers
- Confusing graphite softness with low melting point: Graphite is soft (layers slide) but has a very high melting point (covalent bonds within layers are strong)
- Saying fullerenes are giant covalent: C₆₀ fullerene is a simple molecular structure — it has weak forces between molecules and a relatively low melting point
Practice questions for Giant Covalent Structures
Why do giant covalent structures have very high melting points?
Explain why graphite conducts electricity but diamond does not.
Quick recall flashcards
What are fullerenes?
Hollow carbon cages (like C₆₀) — used to deliver drugs in medicine
What is graphene?
A single layer of graphite — extremely strong, conducts electricity