Nanoparticles are 1 nm to 100 nm in size. They have very large surface area to volume ratios. The properties of nanoparticulate substances are different from those of the same substance in bulk.

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.

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

Particle | Diameter |
---|---|

Atoms and small molecules | 0.1 nm |

Nanoparticles | 1 to 100 nm |

Fine particles (also called particulate matter - PM_{2.5}) | 100 to 2,500 nm |

Coarse particles (PM_{10}, or dust) | 2500 to 10,000 nm |

Thickness of paper | 100,000 nm |

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.

Round each number to 1 significant figure:

30 nm and 0.3 nm

Number of times larger ≈ = 100

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

The symbol ≈ is used to show that the answer is approximate.

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.

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

Surface area = 6 × 10 × 10 = 600 nm^{2} (remember that a cube has six sides)

Volume = 10 × 10 × 10 = 1000 nm^{3}

Surface area to volume ratio = = 0.6