Who this is for: Cambridge IGCSE Chemistry (0620) students who know diamond is hard but cannot explain why graphite conducts electricity or why SiO₂ has such a high melting point.
What query it owns: how to understand and revise giant covalent structures in Cambridge IGCSE Chemistry.
Why this is safe: this page owns the giant-covalent revision-guide angle, while Tutopiya’s Giant Covalent Structures subtopic page owns the learning resource and the free Giant Covalent Structures quiz owns the practice.

Giant covalent structures (macromolecules) are networks where each atom is joined to others by strong covalent bonds throughout the structure — not just within small molecules. Diamond, graphite and silicon dioxide are the key examples in Cambridge IGCSE Chemistry (0620). Properties such as hardness, melting point and electrical conductivity follow directly from how atoms are bonded and arranged.

Key takeaways

• Giant covalent = continuous network of strong covalent bonds → very high melting points.
• Diamond — each C bonded to 4 others tetrahedrally; hard, insulator, no free electrons.
• Graphite — each C bonded to 3 others in layers; soft, conducts (delocalised electrons between layers).
• Silicon dioxide (SiO₂) — similar network to diamond; hard, high melting point, insulator.
• Confirm with the Giant Covalent Structures quiz.

What are giant covalent structures?

Giant covalent structures are substances in which large numbers of atoms are linked by covalent bonds in a continuous three-dimensional network. There are no separate molecules — the entire crystal is one giant structure. Cambridge IGCSE Chemistry (0620) requires you to compare diamond, graphite and silicon dioxide and explain properties from bonding and structure.

Read the full notes on Tutopiya’s Giant Covalent Structures subtopic page.

Diamond vs graphite vs silicon dioxide — comparison table

Structure	Bonding arrangement	Hardness	Conducts electricity?	Melting point
Diamond	C, 4 bonds each, tetrahedral	Very hard	No	Very high
Graphite	C, 3 bonds, layered sheets	Soft (layers slide)	Yes (along layers)	Very high
Silicon dioxide	Si–O network	Hard	No	Very high

Giant covalent vs simple molecular — comparison table

Feature	Giant covalent	Simple molecular
Structure	Continuous network	Discrete molecules
Bonds broken at melting	Many strong covalent bonds	Weak intermolecular forces
Melting point	Very high	Low
Example	Diamond	Iodine

How to answer giant covalent structure questions — step by step

1. Identify the structure — diamond, graphite or SiO₂.
2. Describe bonding — how many bonds per atom, 3D vs layered.
3. For explain questions, link property to structure and bonding (e.g. delocalised electrons → conductivity).
4. Contrast with simple molecular if the question asks compare.
5. Test with the free Giant Covalent Structures quiz.

Past-paper wording: command words that matter

Command word / phrase	What the question wants	Typical stem
Describe	Structure and bonding	”Describe the structure of graphite.”
Explain	Property from structure	”Explain why diamond is hard.”
Compare	Two structures side by side	”Compare diamond and graphite.”
State	Short fact	”State why graphite is used as a lubricant.”

Worked exam-style stems (how to answer the wording)

1. “Explain why diamond has a very high melting point.” Giant covalent structure; each carbon bonded to four others by strong covalent bonds; large amount of energy needed to break many bonds throughout the lattice.
2. “Explain why graphite conducts electricity but diamond does not.” Graphite has delocalised electrons between layers that are free to move and carry charge; diamond has no free electrons — all used in four strong bonds per carbon.
3. “Describe the structure of silicon dioxide.” Each silicon bonded to four oxygen atoms; each oxygen to two silicons; giant covalent network similar to diamond structure.

Practise more on the Atoms topical past paper questions.

How giant covalent structures connect to other bonding types

Giant covalent sits alongside Simple Molecules and Covalent Bonds and Ions and Ionic Bonds in the Atoms unit. Exam compare questions often pit all three structure types. The Cambridge IGCSE Chemistry hub links every bonding subtopic.

Common mistakes students make

• Saying graphite is soft because covalent bonds are weak — layers slide; bonds within sheets are strong.
• Claiming diamond conducts because carbon is a non-metal — diamond has no free electrons.
• Confusing SiO₂ with a simple molecular formula like CO₂ (giant network vs small molecule).
• Explaining high melting point of giant covalent with intermolecular forces — many covalent bonds break.
• Skipping the Giant Covalent Structures quiz.

When you need more support

If compare/explain questions on diamond and graphite keep scoring partial marks, drill the topical past paper questions and book a Cambridge IGCSE Chemistry tutor.

Frequently asked questions

Why is graphite soft but diamond hard? Graphite has layers that slide over each other; diamond has a rigid 3D network of four bonds per carbon.

Does silicon dioxide conduct electricity? No — no free-moving charged particles; it is a giant covalent insulator.

What is the difference between giant covalent and simple molecular? Giant covalent has a continuous network of covalent bonds; simple molecular has separate small molecules with weak forces between them.

How do I revise giant covalent structures effectively? Learn the three key structures, practise describe/explain/compare stems, take the Giant Covalent Structures quiz.

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