Why is "Explaining a giant covalent melting point by saying you overcome 'strong intermolecular forces'" a common mistake in Giant Covalent Structures?

Why it happens: Students copy the simple-molecular explanation and just swap 'weak' for 'strong'. How to avoid it: Giant covalent structures have **no separate molecules**, so there are no intermolecular forces. Melting **breaks the strong covalent bonds** themselves — say 'many strong covalent bonds'. Source: Edexcel Chemistry examiner reports — recurring error

Why is "Saying graphite's layers are held together by 'weak covalent bonds'" a common mistake in Giant Covalent Structures?

Why it happens: Students know covalent bonds are involved and assume the forces between layers must be weak covalent bonds. How to avoid it: Within a layer the bonds are strong covalent bonds; **between layers** there are only **weak forces** (not covalent bonds). It is these weak forces that let layers slide. Source: Edexcel Chemistry examiner reports

Why is "Classifying C₆₀ fullerene as a giant covalent structure" a common mistake in Giant Covalent Structures?

Why it happens: It is a big carbon structure, so students assume it must be giant covalent like diamond/graphite. How to avoid it: C₆₀ is a **single discrete molecule** → **simple molecular** → relatively **low** melting point. Only diamond, graphite and graphene are giant covalent. Source: Edexcel Chemistry examiner reports

Why is "Saying diamond conducts electricity (or not explaining why graphite does)" a common mistake in Giant Covalent Structures?

Why it happens: Students know graphite conducts and over-generalise to all carbon, or forget the delocalised-electron reason. How to avoid it: Diamond uses **all 4 electrons in bonds → no free electrons → no conduction**. Graphite/graphene have **1 delocalised electron per atom, free to move and carry charge → conduct**. Source: Edexcel Chemistry examiner reports

Why is "Writing only 'it has strong bonds' for a high melting point" a common mistake in Giant Covalent Structures?

Why it happens: Students give half the idea and assume the bond strength alone earns the mark. How to avoid it: State **both**: there are **many strong covalent bonds** AND **a large amount of energy is needed to break them**. One half on its own caps the marks. Source: Edexcel Chemistry examiner reports

Why is "Saying graphite conducts because it 'has ions' or because 'electrons flow like in a metal wire'" a common mistake in Giant Covalent Structures?

Why it happens: Conduction is associated with ions (electrolysis) or with metals, so students reach for the wrong reason. How to avoid it: Graphite has **no ions** — it conducts because of **delocalised electrons free to move** within the layers. Name the delocalised electrons specifically. Source: Edexcel Chemistry examiner reports

Covalent bondingEdexcel IGCSE Science(Double Award)-Chemistry (4WSD0-1C)

Giant Covalent Structures

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Giant Covalent Structures — Edexcel International GCSE Science (Double Award) Chemistry (4WSD0-1C) Study Notes

Huge networks of atoms joined by strong covalent bonds throughout — diamond, graphite, graphene, C₆₀ fullerene and silicon(IV) oxide. Why giant covalent structures have very high melting points, why diamond is hard but graphite is soft, and why graphite and graphene conduct electricity while diamond does not. Covers Double Award Chemistry spec 1.65–1.69, assessed on Chemistry Paper 1 (4WSD0/1C).

What you’ll learn

Mapped to the Edexcel IGCSE 4WSD0-1C syllabus (2026 onwards).

1.65 — Explain the high melting points of giant covalent structures.
1.66 — Explain how the structures of diamond, graphite and C60 fullerene relate to their properties.
1.67 — Recall diamond, graphite, graphene and C60 fullerene as allotropes of carbon.
1.68 — Explain why graphite and graphene conduct electricity but diamond does not.
1.69 — Recall that silicon(IV) oxide has a giant covalent structure like diamond.

What is a giant covalent structure? (spec 1.65)

A continuous network of strong covalent bonds → very high melting point.

A giant covalent structure (also called macromolecular) is a huge, continuous network of atoms held together by strong covalent bonds throughout the whole structure. There are no separate molecules — the entire crystal is effectively one giant molecule.

Examples on the Double Award spec. Diamond, graphite, graphene and silicon(IV) oxide (SiO₂ — also called silica, quartz or sand).

Why are the melting points so high?

To melt a giant covalent substance you must break many strong covalent bonds that run right through the structure. Because covalent bonds are strong and there are an enormous number of them, this takes a huge amount of energy — so the melting (and boiling) points are very high, typically well over 2000 °C. Every giant covalent substance is a solid at room temperature.

Compare with simple molecular substances. When you melt a simple molecular substance (like ice or iodine) you only overcome weak forces between the molecules — the covalent bonds inside the molecules are NOT broken — so the melting point is low. In a giant covalent structure there are no weak forces to overcome; you must break the strong bonds themselves.

Melting a giant covalent solid means breaking the strong covalent bonds themselves — not just weak forces between molecules.

Other shared properties. Giant covalent solids are also hard (rigid network of bonds) and insoluble in water — no solvent can break the continuous network. The big exception is graphite, which is soft (explained later).

Giant covalent = continuous network of strong covalent bonds; no separate molecules.
Very high melting point — many strong covalent bonds must be broken.
Contrast: simple molecular melts by overcoming WEAK forces (covalent bonds stay intact) → low m.p.
Generally hard and insoluble (graphite is the soft exception).

See the full worked example for giant covalent structures →

Diamond — hard and non-conducting (spec 1.66, 1.68)

Each carbon bonded to 4 others → very hard, very high m.p., no free electrons → no conduction.

Diamond is a giant covalent form of pure carbon.

Each carbon atom forms 4 strong covalent bonds to 4 other carbon atoms.
The bonds point to the corners of a tetrahedron, building a rigid, continuous 3D lattice.

Why diamond is very hard. Every atom is locked into the rigid 3D network of strong covalent bonds, so the structure strongly resists being deformed. This is why diamond is used in cutting tools, drill tips and saw blades.

Why diamond has a very high melting point. Melting requires breaking many strong covalent bonds throughout the lattice — a huge amount of energy — so the melting point is extremely high (over 3500 °C).

Why diamond does NOT conduct electricity. All four of each carbon's outer electrons are used in covalent bonds. There are no delocalised (free) electrons and no ions — so there are no charge carriers free to move, and diamond cannot conduct.

Every carbon uses all 4 outer electrons in bonds — none are free to carry charge, so diamond does not conduct.

Each carbon forms 4 covalent bonds (tetrahedral) → rigid 3D lattice.
Very hard — used in cutting/drilling tools.
Very high m.p. — many strong covalent bonds to break.
Does NOT conduct — all 4 outer electrons in bonds, no free electrons.

See the full worked example for giant covalent structures →

Graphite — soft and conducting (spec 1.66, 1.68)

3 bonds per carbon in sliding layers; 1 delocalised electron per atom → conducts.

Graphite is another giant covalent form of pure carbon, but the carbon atoms are arranged completely differently from diamond.

Each carbon atom forms only 3 strong covalent bonds to 3 other carbons, making flat layers of joined hexagons (six-membered rings).
Each carbon's fourth outer electron is not used in bonding — it becomes a delocalised electron that is free to move.
The layers are held to each other only by weak forces (not by covalent bonds).

Why graphite is soft / slippery (a lubricant). Because only weak forces hold the layers together, the layers can slide over one another easily. This makes graphite soft and slippery — it is used as a lubricant and as the "lead" in pencils (layers rub off onto the paper).

Why graphite conducts electricity. Each carbon contributes one delocalised electron. These delocalised electrons can move along the layers and carry charge through the structure. Mobile charge carriers = electrical conduction. This is why graphite is used for electrodes (for example in electrolysis).

Why graphite still has a high melting point. Within each layer the carbon atoms are joined by strong covalent bonds, and melting still means breaking many of these strong bonds — so the melting point is very high, like other giant covalent structures.

Graphite keeps one delocalised electron per carbon, free to carry charge — and its layers slide on weak forces, making it soft.

Each carbon forms 3 covalent bonds → layers of hexagons.
Layers held by WEAK forces → slide → soft/slippery → lubricant + pencil lead.
1 delocalised electron per carbon → free to move → CONDUCTS electricity.
Strong bonds within layers → still high melting point.

See the full worked example for giant covalent structures →

Graphene, C₆₀ fullerene and the allotropes of carbon (spec 1.67)

Graphene = one graphite layer; C₆₀ = a simple molecular cage; all four are allotropes of carbon.

Diamond, graphite, graphene and C₆₀ fullerene are all allotropes of carbon — different structural forms of the same element, carbon.

Graphene.

A single layer of graphite — just one atom thick.
Each carbon bonded to 3 others in a flat 2D sheet of hexagons, with 1 delocalised electron per carbon.
So graphene is extremely strong (strong covalent bonds across the sheet) and conducts electricity (delocalised electrons).
Uses: flexible touchscreens, lightweight composites, high-performance electronics.

C₆₀ fullerene (buckminsterfullerene).

A discrete molecule of 60 carbon atoms arranged in a hollow, roughly spherical "football" cage of hexagons and pentagons.
Crucially, C₆₀ is simple molecular, NOT giant covalent: separate C₆₀ molecules are held together by weak forces between the molecules.
So C₆₀ has a low melting point relative to diamond and graphite — you only overcome weak forces between the cage molecules, not strong covalent bonds throughout.
Uses: drug delivery (the hollow cage can carry molecules), lubricants, catalysts.

Why this matters in the exam. A favourite trap is to assume any large carbon structure is giant covalent. C₆₀ is the exception — it is a single molecule, so it is simple molecular and has a comparatively low melting point.

Allotrope	Bonds per C	Structure	Conducts?	Melting point
Diamond	4	giant covalent 3D lattice	No	Very high
Graphite	3	giant covalent layers	Yes	Very high
Graphene	3	single giant covalent layer	Yes	Very high
C₆₀ fullerene	3	simple molecular cage	No	Low (relative)

Allotropes of carbon = diamond, graphite, graphene, C₆₀ fullerene.
Graphene = one graphite layer → strong AND conducts (delocalised electrons).
C₆₀ fullerene = a single molecule → SIMPLE molecular → low m.p. relative to diamond/graphite.
Trap: not every big carbon structure is giant covalent — C₆₀ is the exception.

See the full worked example for giant covalent structures →

Silicon(IV) oxide — diamond-like silica (spec 1.69)

SiO₂ has a giant covalent structure like diamond → high m.p., hard, non-conducting.

Silicon(IV) oxide (SiO₂), also called silica (the main substance in sand and quartz), has a giant covalent structure like diamond.

Each silicon atom is covalently bonded to 4 oxygen atoms, and each oxygen is bonded to 2 silicon atoms.
This builds a rigid, continuous 3D lattice of strong Si–O covalent bonds — just like the tetrahedral network in diamond.

Properties (the same logic as diamond):

Very high melting point — many strong covalent bonds must be broken.
Hard — rigid 3D network of strong bonds.
Does NOT conduct electricity — no delocalised electrons and no ions.
Insoluble in water.

Uses. Glass-making, sandpaper (abrasive), and as the silica in sand.

Exam shortcut. If a question says "silicon(IV) oxide" or "silica", treat it exactly like diamond: giant covalent, high melting point, hard, non-conductor.

SiO₂ = giant covalent structure LIKE DIAMOND.
Each Si bonded to 4 O; each O bonded to 2 Si.
Very high m.p., hard, insoluble, non-conducting.
Treat 'silica' / 'silicon(IV) oxide' just like diamond in answers.

How it’s examined

Double Award Chemistry is assessed on one untiered paper — Chemistry Paper 1 (4WSD0/1C), 2 hours, 110 marks, 33.3% of the Double Award (calculator allowed). Giant covalent structures appear as explain marks: explain the high melting point of a giant covalent substance (break many strong covalent bonds); explain why diamond is hard but graphite is soft; and the classic discriminator — explain why graphite/graphene conduct but diamond does not (delocalised electrons vs all electrons in bonds). You may also be asked to recall the four carbon allotropes or that silicon(IV) oxide is giant covalent like diamond.

Sources: Pearson Edexcel International GCSE Science (Double Award) 4SD0 specification — Issue 4 (valid for 2026 onwards); Pearson Edexcel International GCSE Chemistry 4CH1 specification — Issue 4 (shared Chemistry Paper 1 content); Pearson Edexcel 4SD0 / 4CH1 examiner reports 2022–2024. Last reviewed 2026-06-07.

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Step-by-step worked examples — Giant Covalent Structures

Step-by-step solutions to past-paper-style questions on giant covalent structures, written exactly the way a tutor would explain them at the board.

1Explain the high melting point of a giant covalent structure (Getting started)
Getting started• 4WSD0/1C style — short answer• giant-covalent, spec-1.65
Question
Diamond has a very high melting point. Explain why, in terms of its structure and bonding. (2 marks)
Step-by-step solution
1. Step 1
  Bonding (1). Diamond has many strong covalent bonds holding the atoms together throughout the structure.
2. Step 2
  Energy (1). A large amount of energy is needed to break these many strong covalent bonds, so the melting point is very high.
3. Step 3
  Avoid the trap. Do NOT say 'strong intermolecular forces' — giant covalent structures have no separate molecules. You break covalent bonds, not forces between molecules.
Answer
Diamond is a giant covalent structure with many strong covalent bonds throughout. A large amount of energy is needed to break these strong covalent bonds, so the melting point is very high.
Examiner tip
Two marks: (1) many strong covalent bonds; (2) a lot of energy is needed to break them. The phrase 'covalent bonds' (not 'intermolecular forces') is essential here.
2Classify the carbon allotropes (Getting started)
Getting started• 4WSD0/1C style — short answer• allotropes, spec-1.67
Question
From the list — diamond, graphite, graphene, C₆₀ fullerene — state (a) which are giant covalent structures and (b) which is a simple molecular structure. (2 marks)
Step-by-step solution
1. Step 1
  (a) Giant covalent (1). Diamond, graphite and graphene are all giant covalent — continuous networks of strong covalent bonds.
2. Step 2
  (b) Simple molecular (1). C₆₀ fullerene is a single discrete molecule, so it is simple molecular.
3. Step 3
  Why it matters. This is why C₆₀ has a much lower melting point than diamond or graphite.
Answer
(a) diamond, graphite and graphene are giant covalent; (b) C₆₀ fullerene is simple molecular.
Examiner tip
All four are allotropes of carbon, but only C₆₀ is simple molecular. Students who call C₆₀ 'giant covalent' lose the mark and then wrongly predict a high melting point.
3Link diamond's structure to two properties (Building confidence)
Building confidence• 4WSD0/1C style — structured• diamond, spec-1.66, spec-1.68
Question
Diamond is very hard and does not conduct electricity. Explain both of these properties in terms of its structure and bonding. (4 marks)
Step-by-step solution
1. Step 1
  Hard — structure (1). Each carbon forms 4 strong covalent bonds to other carbons in a rigid 3D lattice.
2. Step 2
  Hard — reason (1). This rigid network of strong bonds strongly resists being deformed, so diamond is very hard.
3. Step 3
  No conduction — electrons (1). All 4 of each carbon's outer electrons are used in covalent bonds.
4. Step 4
  No conduction — reason (1). There are no delocalised (free) electrons (and no ions) to carry charge, so diamond does not conduct.
Answer
Diamond is hard because each carbon forms 4 strong covalent bonds in a rigid 3D lattice that resists deformation. It does not conduct because all the outer electrons are held in covalent bonds, leaving no delocalised electrons to carry charge.
Examiner tip
Two marks for each property: a structure point plus a reason. For conduction, the key phrase is 'no free/delocalised electrons'.
4Explain why graphite is soft and used as a lubricant (Building confidence)
Building confidence• 4WSD0/1C style — structured• graphite, spec-1.66
Question
Graphite is soft and slippery and is used as a lubricant. Explain why, in terms of its structure and bonding. (3 marks)
Step-by-step solution
1. Step 1
  Structure (1). Graphite is made of layers of carbon atoms (each carbon bonded to only 3 others).
2. Step 2
  Forces (1). The layers are held together by weak forces (not by covalent bonds).
3. Step 3
  Reason (1). Because the forces between layers are weak, the layers can slide over each other easily, making graphite soft and slippery.
Answer
Graphite is made of layers held together by weak forces. Because these forces are weak, the layers can slide over one another easily, so graphite is soft and slippery and works as a lubricant.
Examiner tip
Marks are for: layers; weak forces between the layers; layers slide. Do NOT say the weak forces are 'weak covalent bonds' — that is wrong and loses the mark.
5Why graphite conducts but diamond does not (Stretch)
Stretch• 4WSD0/1C style — extended• graphite, diamond, spec-1.68, conductivity
Question
Graphite conducts electricity but diamond does not, even though both are made only of carbon atoms. Explain this difference. (4 marks)
Step-by-step solution
1. Step 1
  Graphite bonding (1). In graphite each carbon forms only 3 covalent bonds, so each carbon has one electron that is not used in bonding.
2. Step 2
  Graphite — delocalised (1). This spare electron becomes a delocalised electron that is free to move along the layers and carry charge → graphite conducts.
3. Step 3
  Diamond bonding (1). In diamond each carbon forms 4 covalent bonds, so all outer electrons are used in bonding.
4. Step 4
  Diamond — no carriers (1). There are no delocalised/free electrons in diamond, so there is nothing to carry charge → diamond does not conduct.
Answer
In graphite each carbon bonds to only 3 others, leaving one delocalised electron per atom that is free to move along the layers and carry charge, so graphite conducts. In diamond each carbon bonds to 4 others, so all electrons are used in bonds — there are no delocalised electrons to carry charge, so diamond does not conduct.
Examiner tip
The discriminating phrase is 'delocalised electrons free to move and carry charge' for graphite, set against 'all electrons used in bonds' for diamond. A complete answer contrasts 3 bonds vs 4 bonds.
6Silicon(IV) oxide compared with diamond (Stretch)
Stretch• 4WSD0/1C style — extended• silica, spec-1.69, spec-1.65
Question
Silicon(IV) oxide (silica) is used to make sandpaper because it is hard and has a very high melting point. Describe its structure and explain these two properties. (4 marks)
Step-by-step solution
1. Step 1
  Structure (1). Silicon(IV) oxide has a giant covalent structure like diamond — each silicon bonded to 4 oxygen atoms (and each oxygen to 2 silicon) in a continuous 3D lattice.
2. Step 2
  Hard (1). The rigid network of strong covalent bonds resists deformation, so it is hard.
3. Step 3
  High m.p. — bonds (1). Melting requires breaking many strong covalent bonds throughout the lattice.
4. Step 4
  High m.p. — energy (1). This needs a large amount of energy, so the melting point is very high.
Answer
Silicon(IV) oxide is giant covalent, like diamond: each silicon is bonded to 4 oxygen atoms in a rigid 3D lattice of strong covalent bonds. This rigid network resists deformation, so it is hard; and melting needs a large amount of energy to break the many strong covalent bonds, so the melting point is very high.
Examiner tip
Credit 'giant covalent like diamond' for structure. The high-m.p. explanation needs both 'many strong covalent bonds' and 'a lot of energy to break them'.

Model Answers — Giant Covalent Structures

High-scoring sample answers for giant covalent structures on the Pearson Edexcel IGCSE Chemistry Paper 1 (4WSD0/1C) paper, with examiner-style notes mapping each response to the mark scheme and assessment objectives.

Question 1
4WSD0/1C style3 marks
Name the four allotropes of carbon and state which one is a simple molecular structure. (3 marks)
Model answer
The four allotropes of carbon are diamond, graphite, graphene and C₆₀ fullerene. (2 — all four named)

C₆₀ fullerene is the simple molecular structure. (1)
Why this scores
Allotropes = different structural forms of the same element. Diamond, graphite and graphene are giant covalent; only C₆₀ fullerene is simple molecular.
Question 2
4WSD0/1C style2 marks
Explain why giant covalent structures such as silicon(IV) oxide have very high melting points. (2 marks)
Model answer
A giant covalent structure has many strong covalent bonds holding the atoms together throughout the structure. (1)

A large amount of energy is needed to break these many strong covalent bonds, so the melting point is very high. (1)
Why this scores
Both marks hinge on 'covalent bonds'. Do not write 'intermolecular forces' — there are no separate molecules in a giant covalent structure.
Question 3
4WSD0/1C style4 marks
Graphite is used both as a lubricant and as the electrodes in electrolysis. Explain, in terms of its structure, why graphite can be used for each of these. (4 marks)
Model answer
As a lubricant:

Graphite is made of layers held together by weak forces. (1)

These layers can slide over each other, making graphite soft and slippery. (1)

As electrodes:

Each carbon bonds to only 3 others, leaving one delocalised electron per carbon. (1)

These delocalised electrons are free to move and carry charge, so graphite conducts electricity. (1)
Why this scores
Two distinct ideas tested from one structure: sliding layers (held by weak forces) for the lubricant; delocalised electrons free to move for conduction. Keep the two explanations separate.
Question 4
4WSD0/1C style4 marks
C₆₀ fullerene has a much lower melting point than diamond, even though both are made of carbon. Explain why. (4 marks)
Model answer
C₆₀ fullerene is simple molecular — it is made of separate C₆₀ cage molecules. (1)

These molecules are held together only by weak forces between the molecules. (1)

Only a small amount of energy is needed to overcome these weak forces, so the melting point is low. (1)

Diamond is giant covalent, so melting it requires breaking many strong covalent bonds, which needs much more energy — giving a much higher melting point. (1)
Why this scores
The contrast must be explicit: C₆₀ overcomes weak forces between molecules (low m.p.); diamond breaks strong covalent bonds (high m.p.). Saying 'C₆₀ has weaker bonds' is wrong — the covalent bonds inside C₆₀ are strong and are not broken on melting.
Question 5
4WSD0/1C style — extended6 marks
Diamond and graphite are both giant covalent forms of carbon, yet diamond is hard and does not conduct electricity while graphite is soft and does conduct. Compare and explain these differences in terms of structure and bonding. (6 marks)
Model answer
Diamond.

Each carbon forms 4 strong covalent bonds in a rigid 3D lattice, which resists deformation, so diamond is hard. (2)

All 4 outer electrons are used in bonding, so there are no delocalised electrons to carry charge — diamond does not conduct. (1)

Graphite.

Each carbon forms only 3 covalent bonds, giving layers held together by weak forces; the layers can slide, so graphite is soft. (2)

Each carbon has one delocalised electron that is free to move along the layers and carry charge, so graphite conducts electricity. (1)
Why this scores
A top-band answer pairs each property with a structural reason and explicitly contrasts 4 bonds (diamond) with 3 bonds (graphite). The conduction marks require 'delocalised electrons free to move' for graphite and 'no free electrons' for diamond.
Question 6
4WSD0/1C style — extended8 marks
Explain how the structure and bonding of (a) diamond, (b) graphite and (c) silicon(IV) oxide each give rise to a high melting point. Then explain why graphene also conducts electricity. (8 marks)
Model answer
(a) Diamond. Each carbon forms 4 strong covalent bonds in a giant 3D lattice; melting requires breaking many strong covalent bonds, needing a large amount of energy → high m.p. (2)

(b) Graphite. Within each layer the carbons are joined by strong covalent bonds; melting still requires breaking many strong covalent bonds, so the m.p. is also very high. (2)

(c) Silicon(IV) oxide. A giant covalent structure like diamond (each Si bonded to 4 O); breaking the many strong Si–O covalent bonds needs a large amount of energy → high m.p. (2)

Graphene conducting. Graphene is a single layer of graphite in which each carbon bonds to only 3 others, leaving one delocalised electron per carbon; these delocalised electrons are free to move across the sheet and carry charge, so graphene conducts. (2)
Why this scores
Each high-m.p. explanation must say 'many strong covalent bonds' + 'a lot of energy to break them' — generic 'strong bonds' alone caps the marks. The graphene mark needs 'delocalised electrons free to move'.

Key Definitions and Keywords — Giant Covalent Structures

Definitions to memorise and the exact keywords mark schemes credit for giant covalent structures answers — sharpened from recent examiner reports for the 2026 Pearson Edexcel IGCSE Chemistry Paper 1 (4WSD0/1C) sitting.

Giant covalent (macromolecular) structure
Examiner keyword
A huge, continuous network of atoms joined by strong covalent bonds throughout, with no separate molecules. Examples: diamond, graphite, graphene, silicon(IV) oxide.
Allotrope
Examiner keyword
A different structural form of the same element. Diamond, graphite, graphene and C₆₀ fullerene are allotropes of carbon.
Diamond
Examiner keyword
A giant covalent allotrope of carbon in which each carbon forms 4 covalent bonds in a rigid tetrahedral 3D lattice. Very hard, very high melting point, does not conduct electricity.
Graphite
Examiner keyword
A giant covalent allotrope of carbon in which each carbon forms 3 covalent bonds, making layers of hexagons. Layers slide (soft); one delocalised electron per atom lets it conduct electricity.
Graphene
A single layer of graphite, one atom thick. Each carbon bonds to 3 others and has one delocalised electron, so graphene is strong and conducts electricity.
C₆₀ fullerene (buckminsterfullerene)
Examiner keyword
A simple molecular allotrope of carbon: a hollow cage molecule of 60 carbon atoms. Has a low melting point relative to diamond and graphite because separate molecules are held by weak forces.
Silicon(IV) oxide (silica, SiO₂)
Examiner keyword
A giant covalent compound with a structure like diamond — each silicon bonded to 4 oxygen and each oxygen to 2 silicon. Hard, very high melting point, non-conducting.
Delocalised electron
Examiner keyword
An outer electron that is not held in a fixed covalent bond and is free to move through the structure to carry charge. Graphite and graphene have one per carbon; diamond has none.
Covalent bond
Examiner keyword
A strong bond formed by a shared pair of electrons between two non-metal atoms. Many of these run throughout a giant covalent structure.
Simple molecular structure
Small, separate molecules held to each other by weak intermolecular forces, giving low melting points. C₆₀ fullerene is the simple molecular form of carbon.

Common Mistakes and Misconceptions — Giant Covalent Structures

The traps other students keep falling into on giant covalent structures questions — taken from recent Pearson Edexcel IGCSE Chemistry Paper 1 (4WSD0/1C) examiner reports and mark schemes — and how to avoid them.

✕Explaining a giant covalent melting point by saying you overcome 'strong intermolecular forces'
Edexcel Chemistry examiner reports — recurring error
Why it happens
Students copy the simple-molecular explanation and just swap 'weak' for 'strong'.
How to avoid it
Giant covalent structures have no separate molecules, so there are no intermolecular forces. Melting breaks the strong covalent bonds themselves — say 'many strong covalent bonds'.
✕Saying graphite's layers are held together by 'weak covalent bonds'
Edexcel Chemistry examiner reports
Why it happens
Students know covalent bonds are involved and assume the forces between layers must be weak covalent bonds.
How to avoid it
Within a layer the bonds are strong covalent bonds; between layers there are only weak forces (not covalent bonds). It is these weak forces that let layers slide.
✕Classifying C₆₀ fullerene as a giant covalent structure
Edexcel Chemistry examiner reports
Why it happens
It is a big carbon structure, so students assume it must be giant covalent like diamond/graphite.
How to avoid it
C₆₀ is a single discrete molecule → simple molecular → relatively low melting point. Only diamond, graphite and graphene are giant covalent.
✕Saying diamond conducts electricity (or not explaining why graphite does)
Edexcel Chemistry examiner reports
Why it happens
Students know graphite conducts and over-generalise to all carbon, or forget the delocalised-electron reason.
How to avoid it
Diamond uses all 4 electrons in bonds → no free electrons → no conduction. Graphite/graphene have 1 delocalised electron per atom, free to move and carry charge → conduct.
✕Writing only 'it has strong bonds' for a high melting point
Edexcel Chemistry examiner reports
Why it happens
Students give half the idea and assume the bond strength alone earns the mark.
How to avoid it
State both: there are many strong covalent bonds AND a large amount of energy is needed to break them. One half on its own caps the marks.
✕Saying graphite conducts because it 'has ions' or because 'electrons flow like in a metal wire'
Edexcel Chemistry examiner reports
Why it happens
Conduction is associated with ions (electrolysis) or with metals, so students reach for the wrong reason.
How to avoid it
Graphite has no ions — it conducts because of delocalised electrons free to move within the layers. Name the delocalised electrons specifically.

Past paper style quiz

Get a report showing which sub-topics you've nailed and which ones still need work.

Giant Covalent Structures — Edexcel International GCSE Science (Double Award) Chemistry (4WSD0-1C) Study Notes

Examples on the Double Award spec. Diamond, graphite, graphene and silicon(IV) oxide (SiO₂ — also called silica, quartz or sand).

Why are the melting points so high?

Melting a giant covalent solid means breaking the strong covalent bonds themselves — not just weak forces between molecules.

Allotrope

Bonds per C

Structure

Conducts?

Melting point

Diamond

giant covalent 3D lattice

Very high

Graphite

giant covalent layers

Yes

Very high

Graphene

single giant covalent layer

Yes

Very high

C₆₀ fullerene

simple molecular cage

Low (relative)

Giant Covalent Structures

Detailed Notes

What you’ll learn

How it’s examined

1Explain the high melting point of a giant covalent structure (Getting started)

2Classify the carbon allotropes (Getting started)

3Link diamond's structure to two properties (Building confidence)

4Explain why graphite is soft and used as a lubricant (Building confidence)

5Why graphite conducts but diamond does not (Stretch)

6Silicon(IV) oxide compared with diamond (Stretch)

Giant covalent (macromolecular) structure

Allotrope

Diamond

Graphite

Graphene

C₆₀ fullerene (buckminsterfullerene)

Silicon(IV) oxide (silica, SiO₂)

Delocalised electron

Covalent bond

Simple molecular structure

✕Explaining a giant covalent melting point by saying you overcome 'strong intermolecular forces'

✕Saying graphite's layers are held together by 'weak covalent bonds'

✕Classifying C₆₀ fullerene as a giant covalent structure

✕Saying diamond conducts electricity (or not explaining why graphite does)

✕Writing only 'it has strong bonds' for a high melting point

✕Saying graphite conducts because it 'has ions' or because 'electrons flow like in a metal wire'

Past paper style quiz

Giant Covalent Structures

Detailed Notes

What you’ll learn

How it’s examined

1Explain the high melting point of a giant covalent structure (Getting started)

2Classify the carbon allotropes (Getting started)

3Link diamond's structure to two properties (Building confidence)

4Explain why graphite is soft and used as a lubricant (Building confidence)

5Why graphite conducts but diamond does not (Stretch)

6Silicon(IV) oxide compared with diamond (Stretch)

Giant covalent (macromolecular) structure

Allotrope

Diamond

Graphite

Graphene

C₆₀ fullerene (buckminsterfullerene)

Silicon(IV) oxide (silica, SiO₂)

Delocalised electron

Covalent bond

Simple molecular structure

✕Explaining a giant covalent melting point by saying you overcome 'strong intermolecular forces'

✕Saying graphite's layers are held together by 'weak covalent bonds'

✕Classifying C₆₀ fullerene as a giant covalent structure

✕Saying diamond conducts electricity (or not explaining why graphite does)

✕Writing only 'it has strong bonds' for a high melting point

✕Saying graphite conducts because it 'has ions' or because 'electrons flow like in a metal wire'

Past paper style quiz