What are nanoparticles, and why does their size make them so useful?
Nanoparticles; their sizes compared with atoms and bulk materials; surface area to volume ratio; uses; and the risks and considerations of nanotechnology.
A focused answer to AQA GCSE Chemistry 4.2.4, covering the size of nanoparticles, how surface area to volume ratio increases as particles get smaller, the uses of nanoparticles, and the risks and ethical considerations of nanotechnology.
Reviewed by: AI editorial process; not yet individually human-reviewed
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What this dot point is asking
AQA wants you to define nanoparticles by their size, compare them with atoms and bulk materials, calculate and explain how surface area to volume ratio changes with size, describe uses of nanoparticles, and discuss the possible risks of nanotechnology. The maths skill (surface area to volume ratio of cubes) and the evaluation skill (weighing benefits against risks) are both examined.
What nanoparticles are
Surface area to volume ratio
For example, a cube of side cm has a surface area of cm and a volume of cm, a ratio of ; halving the side to cm gives a surface area of cm and a volume of cm, a ratio of . Smaller still means an even larger ratio, which is why so much of a nanoparticle's substance is at its surface.
Uses of nanoparticles
The large surface area makes nanoparticles useful and means smaller quantities are needed:
- Catalysts: the large surface area makes reactions efficient with little material.
- Sun creams: better skin coverage and UV protection than larger particles, while staying transparent.
- Medicine: delivering drugs to specific places in the body.
- Electronics and cosmetics: new conductive films and surface materials.
Risks and considerations
Because nanoparticles behave differently from the same material in bulk, and may be absorbed into the body or released into the environment, their long-term effects are not fully understood. AQA expects you to weigh the clear benefits against these uncertain risks rather than simply listing one side. The same property that makes nanoparticles useful, their very large surface area and high reactivity, is also the source of concern: a substance that is safe and unreactive in bulk may behave quite differently at the nanoscale, so testing the bulk material does not guarantee the nanoparticle form is safe. This is why scientists argue for careful, ongoing research before nanoparticles are used widely in products that contact the body or are released into the environment.
Try this
Q1. State the size range of nanoparticles. [1 mark]
- Cue. Between and nm.
Q2. Explain why nanoparticles are good catalysts. [2 marks]
- Cue. A large surface area to volume ratio means more atoms are exposed for reaction.
Q3. Calculate the surface area to volume ratio of a cube of side nm. [2 marks]
- Cue. Surface area ; volume ; ratio .
Exam-style practice questions
Practice questions written in the style of AQA exam questions on this dot point, with worked answer explainers. The year tag is the paper they imitate, not the source.
AQA 20194 marksA cube-shaped particle has sides of length nm. (a) Calculate its surface area to volume ratio. (b) Explain what happens to this ratio as the particle gets smaller, and why this makes nanoparticles useful as catalysts.Show worked answer →
A 4-mark question combining a surface-area-to-volume calculation with an application.
(a) Surface area of a cube nm; volume nm; ratio (2 marks). (b) As the particle gets smaller the surface area to volume ratio increases, so a greater proportion of the atoms are on the surface (1 mark); this means more atoms are exposed and available to take part in reactions, making nanoparticles very effective catalysts that need only small quantities (1 mark).
Markers reward the correct cube formulae and the more-surface-atoms reasoning.
AQA 20213 marksNanoparticles of titanium dioxide are used in some sun creams. Give one advantage of using nanoparticles in this way, and explain one reason why some people are concerned about the use of nanoparticles in products applied to the skin.Show worked answer →
A 3-mark evaluation question.
Advantage (1 mark): nanoparticles give better, more even coverage and effective UV protection while being transparent on the skin (unlike the white of larger particles), and less material is needed. Concern (2 marks): because nanoparticles are so small they may be absorbed through the skin into the body, and because they behave differently from the same material in bulk, their long-term effects on health are not fully known, so the risks are uncertain.
Markers reward a clear benefit and a risk linked to the unknown long-term effects.
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Sources & how we know this
- AQA GCSE Chemistry (8462) specification — AQA (2016)