Nanoparticles

Nanoscience is the study of structures that are between 1 and 100 nanometres (nm) in size. Most nanoparticles are made up of a few hundred atoms.

Comparing sizes

The table shows the sizes of nanoparticles compared to other types of particles.

ParticleDiameter
Atoms and small molecules0.1 nm
Nanoparticles1 to 100 nm
Fine particles (also called particulate matter - PM2.5)100 to 2,500 nm
Coarse particles (PM10, or dust)2500 to 10,000 nm
Thickness of paper100,000 nm

Worked example

A zinc oxide nanoparticle has a diameter of 32 nm. The diameter of a zinc atom is 0.28 nm. Estimate how many times larger the nanoparticle is compared to a zinc atom.

Worked example answer

Round each number to 1 significant figure:

30 nm and 0.3 nm

Number of times larger ≈ \frac{30}{0.3} = 100

The nanoparticle is about 100 times larger than the zinc atom. This is an example of an order of magnitude calculation.

curriculum-key-fact
The symbol ≈ is used to show that the answer is approximate.

Surface area to volume ratios

Nanoparticles have very large surface area to volume ratios compared to the same material in bulk, as powders, lumps or sheets.

For a solid, the smaller its particles, the greater the surface area to volume ratio. If the length of the side of a cube gets 10 times smaller, the surface area to volume ratio gets 10 times bigger.

Worked example

A cube-shaped nanoparticle has sides of 10 nm. Calculate its surface area to volume ratio.

Worked example answer

Surface area = 6 × 10 × 10 = 600 nm2 (remember that a cube has six sides)

Volume = 10 × 10 × 10 = 1000 nm3

Surface area to volume ratio = \frac{600}{1000} = 0.6