Structure and Bonding of Carbon Diamond, Graphite, Graphene and Fullerenes

SPEC 4.2.3.1–4.2.3.3 • PAPER 1

Structure and Bonding of Carbon

One element. Five very different structures: diamond, graphite, graphene, fullerenes, and carbon nanotubes. The 6-mark graphite question is the centrepiece of this lesson.

Why This Lesson Matters

Carbon forms more structures than any other element at GCSE. The same element makes the hardest natural substance (diamond), one of the softest (graphite), the strongest known 2D material (graphene), and hollow molecular cages (fullerenes). This lesson explains how a single tweak to the bonding pattern produces such radically different properties.

EXAMINER PRIORITY POINTS

Diamond: 4 bonds per C — very hard, very high mp, doesn't conduct

Graphite: 3 bonds per C + 1 delocalised electron — conducts, soft & slippery

Graphene: a single layer of graphite — strong, conductive, 1 atom thick

Fullerenes: hollow molecules of carbon (e.g. C₆₀); large surface area; drug delivery uses

Q01.6 (Nov 2021): 6-mark extended response on graphite — both conductivity AND slippery in one answer

THE ONE BIG IDEA

For each structure, the key question is: how many covalent bonds does each carbon atom form? Diamond = 4. Graphite/graphene = 3 (with 1 delocalised electron). That single number drives every property difference.

Key Definitions

Five terms underpin every answer in this lesson. Memorise them word for word.

DIAMOND

A giant covalent structure in which each carbon atom is bonded to 4 other carbon atoms by strong covalent bonds.

GRAPHITE

A giant covalent structure in which each carbon atom is bonded to 3 other carbon atoms in hexagonal layers, with one delocalised electron per atom.

GRAPHENE

A single layer of graphite — a 2D sheet of carbon atoms in hexagonal rings, one atom thick.

FULLERENE

A molecule of carbon atoms shaped like hollow cages or tubes, based on hexagonal rings (and sometimes pentagons or heptagons). Example: buckminsterfullerene, C₆₀.

Diamond — Structure

Diamond is a giant covalent structure in which each carbon atom forms 4 covalent bonds to 4 other carbon atoms. The bonds point to the four corners of a tetrahedron — every carbon is identical.

THE THREE-MARK STRUCTURE-AND-BONDING ANSWER

From P1 Jun 2022 Q03.1 mark scheme — three marks for: (1) "giant structure" (allow "macromolecular" or "(giant) lattice"); (2) "covalent (bonds)"; (3) "four bonds per carbon / atom". All three required.

Diamond — Properties

Three properties — every one follows from the giant covalent network of 4-bonded carbon atoms.

1Very hard — to scratch diamond you must break many strong covalent bonds

2Very high mp/bp — many strong covalent bonds need to be broken to melt

3Does NOT conduct electricity — all 4 outer electrons used in bonding

4Insoluble in water

1Each carbon uses all 4 outer electrons in covalent bonds

2No free electrons available to move

3Cannot carry charge → does not conduct

USES

Diamond's hardness makes it ideal for cutting tools and drill bits. The same property — many strong covalent bonds in 3D — gives both the high melting point and the hardness.

PEE — Diamond High mp

The 3-mark question from P1 Jun 2022 Q03.2. Mark scheme answer below — note this is the same structure as the lesson 2.07 example, but here we add the diamond-specific detail.

Q: Explain why diamond has a very high melting point. 3 MARKS

P

In diamond, the (covalent) bonds are strong.

E

To melt diamond, many of these strong covalent bonds must be broken — every carbon is held to 4 others throughout the giant structure.

E

A lot of energy is required to break that many strong bonds.

EXAMINER ALERT — P1 Jun 2022 Q03.2

Verbatim from the examiner report: "A large number of students contradicted themselves by referring to 'strong intermolecular forces' as well as strong bonds. There are no intermolecular forces in diamond, let alone strong ones."

Critical: The same examiner also notes for Q03.1 that mentioning IMFs in a diamond answer "negated the mark for covalent bonding" — so you don't just lose the IMF point, you lose the covalent bonding mark too. Three marks become one.

"MORE ENERGY" TRAP — P1 Jun 2022 Q03.2

Verbatim from the examiner report: "Students sometimes referred to 'more energy' required to break the bonds. This did not gain credit as there was no idea of what the energy was being compared with."

Use "a lot of energy" (mark scheme phrase). "More energy" is comparative — and demands a comparison context. If you don't say what it is "more than", the mark is lost.

VERBATIM MARK SCHEME (P1 JUN22 Q03.2)

Mark 1: "(covalent) bonds are strong"

Mark 2: "(and many covalent) bonds must be broken"

Mark 3: "(so) a lot of energy is required"

Graphite — Structure

Graphite is a giant covalent structure in which each carbon atom forms 3 covalent bonds to 3 other carbons, arranged in flat hexagonal layers. The 4th outer electron of each carbon is delocalised — free to move along the layer.

THREE STRUCTURAL FACTS THE EXAMINER WANTS

Each carbon forms 3 covalent bonds (not 4 like diamond)

One electron per carbon is delocalised along the layer

Layers held by weak forces only — no covalent bonds between layers

Graphite — Properties From Structure

Two properties of graphite — and the spec demands you explain each in terms of structure and bonding.

1Each C makes 3 bonds → 1 delocalised electron per atom

2Delocalised electrons move along the layers

3Carry electrical charge → graphite conducts

1Layers held only by weak forces between them

2Layers can slide over each other

3Soft and slippery → used as a lubricant; in pencils

HIGH MELTING POINT — DON'T FORGET

Graphite, like diamond, has a very high melting point. Why? The covalent bonds within each layer are strong, and there are many of them. To melt graphite you'd need to break those covalent bonds in the layers — needs lots of energy. The "weak forces between layers" only explain slipperiness, not melting point.

SIMILAR TO METALS

Spec wording: "graphite is similar to metals in that it has delocalised electrons." This is the synoptic link to lesson 2.04/2.07: graphite conducts because of the same delocalised-electron mechanism that makes metals conduct.

Examiner Alert — Graphite Language Traps

The Nov 2021 Q01.6 examiner report gives a complete catalogue of the errors that lose marks on graphite questions.

EXAMINER ALERT — P1 Nov 2021 Q01.6 (full verbatim)

"The reasons for the slipperiness of graphite were better understood than its electrical conductivity, though many did not refer to the weakness of the forces between the layers. There was some poor use of language in the description of the structure, with atoms, molecules and ions being used interchangeably. A fairly common misconception is that there are gaps between the layers, allowing 'electricity' to somehow slip through. Many students did not seem to appreciate that the electric current is delocalised electrons themselves flowing through the structure."

FOUR ERRORS, FOUR FIXES

Wrong (no mark)Right (scores)

"Electricity slips through the gaps between layers""Delocalised electrons themselves flow through the structure / along the layers"

"Electrons move between layers""Delocalised electrons move along the layers"

"Graphite has carbon molecules / ions""Graphite has carbon atoms "

"Covalent bonding" (alone)" Giant structure with covalent bonding"

WHAT IS ELECTRIC CURRENT, EXACTLY?

An electric current IS the movement of charged particles. It's not "something else" passing through gaps. In graphite, the current is literally the delocalised electrons themselves moving along the layers — when you say "graphite conducts", you're saying these electrons flow.

PEE — Why Graphite Conducts but Diamond Does Not

The classic 4-mark application question. Each "side" is worth 2 marks: 1 for the bonding fact, 1 for the consequence.

Q: Explain why graphite can conduct electricity but diamond cannot. 4 MARKS

P

In graphite, each carbon forms only 3 covalent bonds, so one electron per carbon is delocalised.

E

These delocalised electrons can move along the layers and carry electrical charge — so graphite conducts.

P

In diamond, each carbon forms 4 covalent bonds — so all 4 outer electrons are used in bonding.

E

There are no free / delocalised electrons in diamond, so no charged particles can move — diamond cannot conduct.

MARK ALLOCATION

Mark 1: graphite — 3 bonds per C / 1 delocalised electron per C

Mark 2: graphite — delocalised electrons carry charge along layers

Mark 3: diamond — 4 bonds per C / all 4 outer electrons used in bonding

Mark 4: diamond — no free electrons / cannot carry charge

PEE — Graphite Soft and Slippery

The 2-mark application question. Mark scheme accepts the structural fact + the consequence.

Q: Explain why graphite is soft and slippery. 2 MARKS

P

Between the hexagonal layers there are only weak forces (no covalent bonds).

E

The layers can therefore slide over each other easily — making graphite soft and slippery.

Common Error

Students sometimes write "the covalent bonds between layers are weak" — wrong. There are no covalent bonds between layers; the layers are held only by weak intermolecular-style forces. Don't invent bonds that aren't there.

USES OF GRAPHITE

Pencils (layers slide off onto paper); industrial lubricants; electrodes in electrolysis (combines slipperiness, conductivity, and high mp).

Graphene

Graphene is a single layer of graphite — one atom thick. Same hexagonal arrangement, same 3 covalent bonds per carbon, same one delocalised electron per atom — just no other layers above or below.

1Strong — covalent bonds within the layer; high tensile strength

2Conducts electricity — delocalised electrons

3Very low mass per area; one atom thick

4Uses: electronics, composites, sensors

Fullerenes

Fullerenes are molecules of carbon arranged in hollow shapes — spheres, ellipsoids, or tubes — built from hexagonal rings (and sometimes pentagons or heptagons).

SPEC FACTS

C₆₀ (buckminsterfullerene) — the first fullerene discovered; 60 carbon atoms in a hollow sphere

Other fullerenes (e.g. C₇₀) have different numbers of atoms and shapes

Hollow molecules — they have an empty space inside the cage

Built mostly from hexagonal rings (with pentagons to allow curvature)

Fullerene Uses & Carbon Nanotubes

From the Nov 2021 Q01.2 mark scheme — any one of these is a 1-mark answer to "give one use of a fullerene":

USES (FROM AQA MARK SCHEME)

Drug delivery (around the body) — drugs trapped inside the cage

Hydrogen storage

Anti-oxidants

Reduction of bacterial growth

Catalysts

Lubricants (spherical fullerenes)

Strengthening materials (cylindrical fullerenes / nanotubes)

CARBON NANOTUBES

Cylindrical fullerenes with a very high length-to-diameter ratio

Very strong along the tube axis (used in high-strength composites)

Conduct electricity (delocalised electrons, like graphite)

Used in: nanotechnology, electronics, sports equipment, strengthening materials

DRUG DELIVERY — TWO TRAPS (P1 Jun 2022 Q03.4 + P1 Nov 2021 Q01.2)

Mark scheme verbatim:"ignore references to ease of movement around the body." The C₆₀ molecule isn't useful for drug delivery because it "moves easily" — it's useful because it is hollow (a cage), unreactive, non-toxic, and has a large surface area to volume ratio.

Examiner report on Q01.2 (fullerene uses): "There were, however, some vague answers such as 'in medicine'." "In medicine" is too vague — name a specific use: drug delivery, catalyst, lubricant, or strengthening material.

Examiner Alert — Two More Traps

EXAMINER ALERT — P1 Nov 2021 Q01.1 (fullerene shape)

Verbatim from the examiner report: "Some focused on the hexagonal arrangement of bonds rather than the molecule as a whole. Others did not appear to realise the shape is three dimensional and described the molecule as a circle." Mark scheme accepts "spherical" or "ball-shaped"; explicitly ignores "round" and "circular".

EXAMINER ALERT — P1 Jun 2022 Q03.1 (no IMFs in diamond)

Verbatim from the examiner report: "Although the majority of students mentioned covalent bonding, many contradicted themselves by referring to intermolecular forces; these are not present in diamond and negated the mark for covalent bonding ." Mention IMFs in a giant covalent answer and the examiner cancels your other marks too.

QUICK SHAPE CHECK

Fullerene C₆₀ → spherical / ball-shaped (3D, hollow)

Carbon nanotube → cylindrical (3D, hollow)

Graphene → 2D sheet (1 atom thick)

Diamond → tetrahedral 3D network

Graphite → layered hexagonal sheets

6-Mark Question — Graphite Properties

This is the centrepiece question of this lesson — P1 Nov 2021 Q01.6. The mark scheme asks for a Level-3 logically-linked account covering BOTH conductivity AND slipperiness.

a good electrical conductor

soft and slippery

6 MARKS

Indicative content (verbatim from MS) — hit ~6 of these for Level 3

STRUCTURE

Bonds are covalent; giant / macromolecular structure; three covalent bonds per carbon atom (or "only three electrons per C used in bonding"); layered structure of (interlocking) hexagonal rings.

CONDUCTS

One electron per carbon is delocalised; these delocalised electrons can move through the structure, carrying electrical charge — so graphite conducts electricity.

SLIPPERY

Weak (intermolecular) forces between layers (or "no covalent bonds between layers"); so the layers can slide over each other — graphite is soft and slippery.

SCAFFOLD FOR YOUR ANSWER

Open with structure (giant / covalent / 3 bonds per C / hexagonal layers). Then split: "Graphite conducts because delocalised electrons move along the layers carrying charge." Then: "Graphite is slippery because weak forces between layers allow them to slide." Two property → mechanism chains, both anchored in the same structure.

Five Carbon Structures — Master Table

StructureBonds per CConducts?Other notable property

Diamond4No (no free electrons)Very hard; very high mp

Graphite3 + 1 delocalised electronYes (along layers)Soft & slippery; very high mp

Graphene3 + 1 delocalised electronYesSingle layer, 1 atom thick; very strong; very low mass

Fullerene (C₆₀)3 (each C in cage)(Limited)Hollow molecule; can trap other molecules — drug delivery

Carbon nanotube3 (each C in tube wall)Yes (along tube)Cylindrical; very strong; high length:diameter ratio

PATTERN TO MEMORISE

4 bonds per carbon = no spare electron = diamond pattern (hard, no conduction). 3 bonds per carbon = 1 spare electron per C = graphite/graphene/nanotube pattern (conducts). Fullerenes and nanotubes are essentially "graphite layers" wrapped into curved shapes.

Practice Question

Diamond and graphite are both forms of carbon, but they have very different properties.

(a) State the number of covalent bonds formed by each carbon atom in diamond and in graphite. 2 MARKS

(b) Explain, in terms of structure and bonding, why graphite is used as an electrode in electrolysis but diamond is not. 3 MARKS

(a) Bond counts — 2 marks:

1

In diamond, each carbon atom forms 4 covalent bonds.

2

In graphite, each carbon atom forms 3 covalent bonds.

(b) Electrode reasoning — 3 marks:

P

Electrodes must conduct electricity to allow current to flow.

E

In graphite, each carbon forms only 3 covalent bonds — one electron per carbon is delocalised and can move along the layers carrying charge — so graphite conducts.

E

In diamond, each carbon forms 4 covalent bonds — all 4 outer electrons are used in bonding, so there are no free electrons, so diamond cannot conduct and cannot be used as an electrode.

SYNOPTIC LINK

Graphite electrodes are used in electrolysis. The link: graphite's combination of conductivity + very high melting point + chemical inertness makes it ideal for electrolysis at high temperatures, such as the extraction of aluminium from molten aluminium oxide.

Summary

Five Forms of Carbon — Key Numbers & Shapes

Diamond: 4 bonds per C, tetrahedral 3D giant covalent network → hard, very high mp, no conduction.

Graphite: 3 bonds per C in hexagonal layers + 1 delocalised electron per C; weak forces between layers → conducts (along layers), soft & slippery (between layers), very high mp.

Graphene: single layer of graphite; 2D, 1 atom thick; very strong, conducts.

Fullerenes: hollow molecules of C (e.g. C₆₀, "buckminsterfullerene") with hexagonal/pentagonal rings; spherical or cage-shaped; uses include drug delivery.

Carbon nanotubes: cylindrical fullerenes; very strong, conduct along tube axis.

DIAMOND (3-MARK STRUCTURE)

(1) Giant structure; (2) covalent bonds; (3) 4 bonds per carbon.

GRAPHITE 6-MARK ESSAY

Structure first (giant covalent / 3 bonds / hexagonal layers); then conductivity (delocalised electrons along layers); then slipperiness (weak forces between layers / layers slide).

EXAM TIP — THE THREE LANGUAGE TRAPS

(1) Diamond has no IMFs — never mention intermolecular forces in a diamond answer. (2) Electrons move ALONG layers in graphite, never "between layers". (3) Graphite has carbon ATOMS — not "molecules" or "ions". And remember: fullerene C₆₀ is "spherical" (3D), never "circular" (2D).