Nanoparticles are increasingly being used in sunscreens and in medical drug delivery systems. Describe two properties of nanoparticles that make them useful in these applications, and for each property explain why it arises.

Edexcel GCSE Chemistry (1CH0) — 9.2 Bulk and surface properties of matter, including nanoparticles (Chem only) · Describe · 4 marks · View as Markdown

Written & reviewed by James Millett — Biology (Imperial College London), PGCE Science (University of Cambridge).

Nanoparticles are particles with diameters between 1 nm and 100 nm. Scientists are developing new uses for nanoparticles in medicine and cosmetics because of the special properties they possess compared to bulk materials.

Model answer (4 marks)

1. Large surface area to volume ratio – the small size gives a high proportion of atoms on the surface, so more of the particle can interact with its surroundings. 2. Enhanced reactivity – the high surface area means the particles can absorb UV light more efficiently (useful in sunscreens) or release drug molecules more readily (useful in drug delivery). 3. Size‑dependent optical properties – at the nanoscale the electronic structure changes, giving new colours or UV‑blocking abilities. 4. Quantum or surface effects – because the particle size is comparable to atomic dimensions, quantum confinement and surface chemistry dominate, producing properties that differ from the bulk material.

Examiner tips

  • Use the exact phrase ‘large surface area to volume ratio’ and link it to increased interaction. Include the two applications (UV absorption, drug release) to show relevance. Mention ‘size‑dependent optical properties’ and ‘quantum effects’ to cover the second property. Keep each point brief but complete.

Common mistakes

  • Mixing up bulk and nanoparticle properties; forgetting to explain why the property arises. Using vague terms like ‘small size’ without mentioning surface area or quantum effects. Writing too long or including irrelevant details such as manufacturing processes.

Mark scheme (4 marks)

  1. Nanoparticles have a very large surface area to volume ratio (compared to bulk material of the same substance)
  2. This large surface area to volume ratio means more of the substance is exposed / available to interact, making nanoparticles more reactive or more effective at absorbing UV radiation / delivering drugs to target cells
  3. Nanoparticles can exhibit different / new properties compared to the bulk material of the same substance (e.g. different optical, chemical or physical properties)
  4. These different properties arise because at the nanoscale the size of the particles is comparable to the scale of atoms/molecules, so quantum or surface effects become significant, meaning behaviour differs from a bulk sample

Key terms in this question

nanoparticles · properties

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