Structure and Properties — NanoparticlesAQA GCSE Chemistry: Revision notes
Section 1
What are nanoparticles?
Nanoparticles are extremely small particles, between 1 and 100 nanometres in size.
- 1 nanometre = 1 × 10⁻⁹ m (one billionth of a metre)
- Each nanoparticle contains a few hundred to a few thousand atoms
- They are smaller than fine particles (PM2.5) but larger than individual atoms
- A human hair is about 80,000 nm wide — nanoparticles are far too small to see
Scale comparison:
| Object | Size |
|---|---|
| Atom | ~0.1 nm |
| Nanoparticle | 1–100 nm |
| Virus | ~100 nm |
| Human hair | ~80,000 nm |
Section 2
Why nanoparticles behave differently
Nanoparticles have very different properties from the same material in bulk because of their enormous surface area to volume ratio.
- As particles get smaller, the ratio of surface area to volume increases dramatically
- A greater proportion of atoms are on the surface rather than inside
- Surface atoms are more reactive than atoms buried inside the bulk
- This means nanoparticles of gold, silver, titanium etc. behave very differently from their bulk forms
Example: Bulk gold is chemically unreactive and yellow. Gold nanoparticles are highly reactive and appear red or blue in solution.
Exam questions almost always ask you to explain why nanoparticles have different properties. The answer is always: very high surface area to volume ratio — more atoms are exposed on the surface, making the material more reactive.
Section 3
Uses of nanoparticles
The unique properties of nanoparticles make them useful across many industries:
| Use | Material | Why |
|---|---|---|
| Sunscreen | TiO₂ or ZnO nanoparticles | Absorb UV, transparent (not white) |
| Antibacterial surfaces | Silver nanoparticles | Toxic to bacteria at low concentrations |
| Drug delivery | Various | Can target specific cells, cross cell membranes |
| Electronics | Carbon nanotubes | Excellent conductors, very strong |
| Catalysts | Platinum, gold nanoparticles | Large surface area increases reaction rate |
| Sports equipment | Carbon nanotubes | Strong but lightweight |
- Nanoparticles are used in clothing, food packaging, medical implants, and cosmetics
Sunscreen: Traditional zinc oxide sunscreen appears white on skin because bulk ZnO particles reflect visible light. ZnO nanoparticles are so small they no longer reflect visible light — the sunscreen becomes transparent — while still absorbing harmful UV radiation.
Section 4
Risks and concerns
The same properties that make nanoparticles useful also raise concerns about their safety:
- Health: Nanoparticles can penetrate cell membranes and enter the bloodstream — long-term health effects are not fully understood
- Lungs: Inhaled nanoparticles can pass into lung tissue and potentially reach the brain
- Environment: Nanoparticles released into soil and water may harm ecosystems — silver nanoparticles can kill beneficial bacteria
- Regulation: Rules around the use of nanoparticles are still being developed — there is ongoing scientific debate
The key tension: Nanoparticles offer real benefits, but their risks are not yet fully known. More research is needed.
Evaluate questions about nanoparticles often ask for both benefits and risks. Benefits: targeted drug delivery, UV protection, antibacterial properties. Risks: unknown long-term health effects, environmental contamination, ability to cross cell membranes.
Must Know
- Nanoparticles are 1–100 nm in size (1 nm = 1 × 10⁻⁹ m)
- Different properties from bulk materials because of very high surface area to volume ratio
- More surface atoms = more reactive
- Uses: sunscreen (TiO₂/ZnO), antibacterial (silver), drug delivery, electronics (carbon nanotubes), catalysts
- Risks: unknown long-term health effects, can cross cell membranes, environmental concerns
- Carbon nanotubes: cylindrical carbon structures — very strong and conduct electricity
That's the notes covered.
Carry on to the next subtopic.