Nanoparticles

Nanoparticles are structures, 1-100 nanometres (nm) in size, that usually contain only a few hundred atoms. This means that nanoparticles are around 100 times larger than atoms and simple molecules.

curriculum-key-fact
1 nm is 1 x 10-9 m (or 0.000,000,001 m).

Buckminsterfullerene, with the formula C60, is a nanoparticle:

Covalent structure of buckminsterfullerene

Small size

Some of the properties of nanoparticles depend on their very small size.

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.

To help with this estimate, round each number to 1 significant figure:

30 nm and 0.3 nm

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

The nanoparticle is about 100 times larger than the zinc atom.

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

Surface area to volume ratios

Some of the properties of nanoparticles depend on their large surface area to volume ratios. For solid substances, the smaller its particles, the greater the surface area to volume ratio.

Worked example

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

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{\textup{600}}{\textup{1000}}

= 0.6

Question

A cube-shaped nanoparticle has sides of 1 nm. Calculate its surface area to volume ratio.

Surface area = 6 × 1 × 1 = 6 nm2

Volume = 1 × 1 × 1 = 1 nm3

Surface area to volume ratio = \frac{\textup{6}}{\textup{1}}

= 6