This mini-lesson covers the whole of CCEA Materials (Unit 1.4 — Nanoparticles): what a nanoparticle is, its surface area to volume ratio, why nanoparticles behave differently from the bulk material, and the benefits and risks of nanoparticles in sun creams.
Work through each screen, answer the questions as you go (some are wordy, some are calculations) and collect ⭐ stars. Press Start when you're ready.
1.4.1 · What is a nanoparticle?
Nanoparticles are tiny
A nanoparticle is a structure that is 1–100 nm in size and contains only a few hundred atoms.
One nanometre (nm) is 0.000 000 001 m = 1 × 10−9 m.
Bulk materials — lumps and powders — consist of huge numbers of atoms.
Nanoparticles sit between individual atoms and bulk powders on the size scale.
A nanoparticle is much bigger than a single atom but far smaller than a grain of bulk powder.
Watch out: "nano" describes size, not a new element. A gold nanoparticle is still gold — it simply behaves differently because it is so small.
Quick check
How big is a nanoparticle?
?Which statement correctly describes a nanoparticle?
1.4.2 · Surface area to volume
Small means huge surface area
The key idea for nanoparticles is the surface area to volume ratio. Compare two cubes:
As the side of a cube decreases by a factor of 10, the surface area to volume ratio increases by a factor of 10.
Why? The numbers (CCEA's cube example)
Large cube (side 100 cm): SA = 6 × 100² = 60 000 cm²; V = 100³ = 1 000 000 cm³ → SA:V = 0.06
Small cube (side 10 cm): SA = 6 × 10² = 600 cm²; V = 10³ = 1000 cm³ → SA:V = 0.6
Side ÷ 10 → ratio × 10. Nanoparticles are so small they have an enormous surface area to volume ratio.
Watch out: the ratio goes up as the particle gets smaller — a common slip is to think a bigger lump has more surface "per volume". It is the other way round.
Calculate
Your turn — surface area : volume
1A cube has sides of 2 cm. Calculate its surface area to volume ratio (surface area ÷ volume), giving your answer per cm.
per cm
Hint: SA = 6 × 2² = 24 cm². Volume = 2³ = 8 cm³. Ratio = 24 ÷ 8.
Quick check
The factor-of-10 rule
?The side length of a cube-shaped particle is decreased by a factor of 10. What happens to its surface area to volume ratio?
1.4.3 · Different properties
Why nanoparticles behave differently
Nanoparticles have different properties from the same material in bulk — and the reason is always the same: their high surface area to volume ratio.
In a nanoparticle a far greater fraction of atoms sit on the surface, where they can react and interact.
More atoms exposed at the surface → nanoparticles are often more reactive and make good catalysts.
They can show different optical or electrical behaviour from the bulk material.
Key sentence for the exam: nanoparticles have properties different from the same material in bulk because of their high surface area to volume ratio.
Quick check
Same gold, different behaviour
?Why do nanoparticles of gold have different properties from a large lump of gold?
1.4.4 · Nanoparticles in sun creams
A real use: sun creams
Sun creams protect skin by absorbing the Sun's ultraviolet (UV) radiation. Many older creams used bulk zinc oxide, which works but is hard to rub in and leaves a white film. Nanoparticles of zinc oxide are now widely used instead.
A thin layer of zinc oxide nanoparticles absorbs UV but is clear on the skin.
Benefits of nanoparticles in sun creams:
Better skin coverage — the cream spreads more evenly.
More effective protection from the Sun's UV rays.
They are clear and colourless, so the cream is invisible on the skin.
Risks to weigh against those benefits:
Potential cell damage — they are so small they may penetrate cell membranes or be breathed in, and may be more toxic than the bulk material.
Harmful effects on the environment.
Exam command word: "evaluate" means weigh the benefits against the risks — give both sides, not just one.
Sort it
Benefit or risk?
For each statement about nanoparticles in sun cream, tap whether it is a benefit or a risk.
Quick check
Choosing the sun cream
?A company switches from bulk zinc oxide to zinc oxide nanoparticles in its sun cream. Which is a genuine benefit of this change?
Match-up
Match the term to its meaning
Tap a term on the left, then its correct meaning on the right.
Recap
The Materials facts to know
Size: a nanoparticle is 1–100 nm and has a few hundred atoms.
Surface area : volume: as the side of a cube ÷10, the SA:V ratio ×10.
Why different: nanoparticles differ from the bulk material because of their high SA:V ratio.
Sun-cream benefits: better coverage, more effective UV protection, invisible (clear/colourless).
Sun-cream risks: possible cell damage, harm to the environment.
You've covered all four CCEA Materials statements (1.4.1–1.4.4). Press Finish to see your score.
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