The table shows the sizes of nanoparticles compared to other types of particles.
|Atoms and small molecules||0.1 nm|
|Nanoparticles||1 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 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.
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 nm2 (remember that a cube has six sides)
Volume = 10 × 10 × 10 = 1000 nm3
Surface area to volume ratio = = 0.6