Nanoparticles

Theory · read, then commit

Nanoparticles are tiny particles 1–100 nm across (1 nm = 1×10⁻⁹ m), containing a few hundred to a few thousand atoms. At this scale a material can behave very differently from its bulk form.

🟡Bulk gold

ColourYellow

ReactivityLow — unreactive with most chemicals

Melting point1064 °C

🔴Gold nanoparticles

ColourRed / purple

ReactivityMuch higher

Melting pointMuch lower

Same gold atoms — but a huge surface-area-to-volume ratio means far more atoms sit on the surface, so reactivity shoots up.

Checkpoint · quick check

Describe what happens to a particle's surface-area-to-volume ratio as the particle gets smaller.

⚠️ Common Mistake

Students often think that a nanoparticle of gold must be a different substance from ordinary gold because its colour and reactivity are so different. It is the same substance — the same gold atoms. What changes is the scale: nanoparticles have a far larger surface-area-to-volume ratio, so a much greater fraction of their atoms sit on the surface, which changes their properties.

▦Graphene

A single layer of graphite, one atom thick — extremely strong, very light, and conducts electricity.

⚽Buckminsterfullerene (C₆₀)

60 carbon atoms in a hollow sphere ('buckyball') — can cage molecules; used in drug delivery and lubricants.

🛢️Carbon nanotube

A rolled-up graphene sheet forming a hollow tube — very strong along its length and conducts electricity.

✅Uses of nanoparticles

Sunscreen: TiO₂ nanoparticles are transparent but still block UV.

Antibacterial: silver nanoparticles — high surface area → very reactive against bacteria.

Catalysis: a high surface area makes them very effective catalysts.

Drug delivery: they can carry medicine directly to target cells.

Checkpoint · quick check

Silver nanoparticles are added to wound dressings. Suggest why their small size makes them suitable for this use.

⚠️ Risks — why more research is needed

Nanoparticles are so small they may pass through cell membranes, be breathed deep into the lungs, and persist in the environment and food chains. Their long-term health and environmental effects are not yet fully understood.

Retrieval · Match the Carbon Nanostructure

⭐ Higher Tier Only

Calculate surface area to volume ratio for different particle sizes — explain why nanoparticles have higher reactivity. Evaluate uses: TiO₂ in sunscreen (transparent at nanoscale, blocks UV), silver nanoparticles (antibacterial). Evaluate risks: potential to penetrate cell membranes, unknown long-term effects, persistence in environment.

Test yourself · 9 questions, exam order

⭐Examiner Tip

When asked why nanoparticles behave differently from the bulk material, the marks are for the surface-area-to-volume ratio — say a much greater fraction of the atoms sit on the surface. Never write that it is a "different substance": it is the same atoms at a smaller scale.

0 of 9 answered

Warm-up · 2 questions

Explain why nanoparticles have different properties from the same material in bulk (large-scale) form.

Suggest why nanoparticles may pose a greater health risk than the same material in larger particle form.

Exam standard · 4 questions

Explain why nanoparticles make very effective catalysts.

Titanium dioxide nanoparticles are used in sunscreen. Suggest why the nanoparticle form is used instead of bulk titanium dioxide.

Explain, using surface-area-to-volume ratio, why nanoparticles are often much more reactive than the same material in bulk.

As the side length of a cube-shaped particle is halved, deduce what happens to its surface-area-to-volume ratio.

Stretch · 3 questions

Evaluate the use of silver nanoparticles in wound dressings by giving one benefit and one risk.

Graphene is one atom thick and conducts electricity. Explain, in terms of its structure, why it is both very strong and a good electrical conductor.

A cube-shaped particle of side 2 nm and one of side 20 nm are compared. Deduce which has the greater surface-area-to-volume ratio, and explain.

Key note · cover it, say it, check it

Revision card · 6 steps Nanoparticles

01Nanoparticles: 1–100 nm.
02Huge surface area to volume ratio → different properties, higher reactivity.
03Graphene: single layer of graphite, strong, conducts.
04Fullerenes (C₆₀): hollow carbon spheres, drug delivery.
05Nanotubes: rolled graphene, strong conductors.
06Risks: may penetrate cells, unknown long-term effects.

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