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This lesson covers nanoparticles — very small particles with dimensions in the range 1–100 nm — and their properties, applications and associated concerns. This is part of the Edexcel GCSE Chemistry (1CH0) specification on Structure, Bonding and Properties.
Nanoparticles are particles that have dimensions (diameter) in the range of 1–100 nanometres (nm).
To put this in perspective:
| Scale | Size |
|---|---|
| 1 nm (nanometre) | 1 × 10⁻⁹ m |
| 1 nm | About 10 atoms lined up in a row |
| Nanoparticle range | 1–100 nm |
| Human hair diameter | ~80,000 nm |
| Typical atom | ~0.1–0.3 nm |
Nanoparticles contain a few hundred to a few thousand atoms. They are much smaller than fine powders (which have particles of about 1,000–10,000 nm) and bulk materials.
| Type | Approximate Diameter | Number of Atoms |
|---|---|---|
| Single atom | 0.1–0.3 nm | 1 |
| Nanoparticle | 1–100 nm | Hundreds to thousands |
| Fine powder | 100–10,000 nm | Millions |
| Coarse/bulk material | > 10,000 nm | Billions+ |
Exam Tip: If asked to define nanoparticles, always state the size range: 1–100 nm. This is a key marking point.
The most important feature of nanoparticles is their very high surface area to volume ratio compared to larger particles of the same material.
As particles get smaller, the proportion of atoms at the surface increases dramatically. Atoms on the surface are more reactive (they are exposed) than atoms buried inside the particle. Therefore:
For a cube with side length L:
This shows that as L gets smaller, the ratio gets larger.
Example calculation:
| Cube Side Length | Surface Area (6L²) | Volume (L³) | SA:V Ratio (6/L) |
|---|---|---|---|
| 1 cm | 6 cm² | 1 cm³ | 6 : 1 |
| 1 mm = 0.1 cm | 0.06 cm² | 0.001 cm³ | 60 : 1 |
| 1 µm = 0.0001 cm | 6 × 10⁻⁸ cm² | 10⁻¹² cm³ | 60,000 : 1 |
| 1 nm = 10⁻⁷ cm | 6 × 10⁻¹´ cm² | 10⁻²¹ cm³ | 60,000,000 : 1 |
The surface area to volume ratio increases enormously as the particle gets smaller.
Exam Tip: You may be asked to calculate the surface area to volume ratio for cubes or compare ratios for different-sized particles. Remember: smaller = bigger ratio.
Because of their high surface area to volume ratio, nanoparticles have different properties from the same material in bulk:
| Property | Nanoparticle vs Bulk |
|---|---|
| Colour | May be different (e.g. gold nanoparticles appear red/purple, not gold) |
| Reactivity | More reactive (more surface atoms available for reactions) |
| Melting point | May be lower than bulk (surface atoms less tightly bound) |
| Catalytic activity | Better catalysts (high surface area means more active sites) |
| Strength | Can be stronger per unit mass |
| Electrical properties | May differ (quantum effects at nanoscale) |
Nanoparticles are a relatively new technology, and there are concerns about their safety:
| Concern | Details |
|---|---|
| Health risks | Nanoparticles are small enough to enter cells and potentially cause damage. Inhaled nanoparticles could cause lung damage. |
| Environmental impact | Nanoparticles released into the environment could accumulate in food chains or contaminate water. |
| Unknown long-term effects | Because nanoscience is relatively new, the long-term effects on health and the environment are not yet fully understood. |
| Regulation | There is debate about how nanoparticles should be regulated and tested before use in consumer products. |
| Ethical concerns | Should products containing nanoparticles be clearly labelled? Do consumers have enough information? |
Exam Tip: If asked about the risks of nanoparticles, give specific concerns (e.g. may enter cells, may damage lungs) and mention that long-term effects are not fully known.
Question: A cubic particle has side length 2 cm. A second cubic particle has side length 0.2 cm. Calculate the surface area to volume ratio for each cube and comment on how the ratio changes.
Answer:
Cube A (side = 2 cm):
Cube B (side = 0.2 cm):
Comment: As the side length decreases by a factor of 10, the surface area to volume ratio increases by a factor of 10 (from 3:1 to 30:1). Smaller particles have a much larger proportion of their atoms at the surface.
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