Bulk and Surface Properties of Matter Including Nanoparticles — AQA GCSE Chemistry (Separate)
The properties of a material can depend on its particle size, especially at the nanoscale.
Bulk properties
The bulk material is the substance in its normal, large-scale form. Its properties (e.g. melting point, strength, colour) depend on its structure and bonding.
Why size matters: surface area to volume ratio
As particles get smaller, a greater proportion of their atoms are on the surface, so the surface area to volume ratio increases. At the nanoscale (1–100 nm) this ratio becomes very large.
A large surface area to volume ratio means:
- the material can behave differently from the bulk form, and
- less material is needed to be effective (important for catalysts).
The size relationship
If the length of the side of a cube decreases by a factor of 10, the surface area to volume ratio increases by a factor of 10.
Consequences
Nanoparticles can have new and useful properties, leading to uses in catalysts, sun creams, medicine and electronics. However, because they are so different and small, their potential risks to health and the environment are not yet fully understood.
Exam tips
- Explain how decreasing particle size increases the surface area to volume ratio.
- A large ratio means different properties and less material needed.
- Practise the cube calculation (÷10 side → ×10 ratio).
- Note the uses and the uncertainty about risks.