Nanoparticle size and surface area

By UK GCSE Chemistry · independent study · myAudience

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Nanoparticle size and surface area

Nanoparticles are commonly described in this course as particles roughly 1–100 nm across. A nanometre is 10⁻⁹ m. This range is much smaller than an ordinary grain visible to the unaided eye, but particles in it still have many atoms rather than necessarily being single atoms.

For a cube of side length L, surface area is 6L² and volume is L³, so their ratio is 6/L. Smaller cubes therefore have more surface area relative to their volume. A high proportion of atoms can be near a surface, making surface interactions especially important.

Nanoparticle properties can differ from those of larger pieces of the same substance. Shape, composition, coating and surrounding conditions also matter. A size label alone does not prove a particular effectiveness or hazard; measurements need an actual material and exposure context.

Worked example: Compare surface-area-to-volume ratios for cubes of side 2 units and1unit.

For side 2: area 24, volume 8, ratio 3.

For side 1: area 6, volume 1, ratio 6.

Halving length doubles the ratio for this geometry.

Answer: The smaller cube has twice the surface-area-to-volume ratio.

Check your understanding: Why is nm not the same as μm?

Answer: 1 μm equals 1000 nm.

Why: The prefixes differ by a factor of 1000, so confusing them causes a large scale error.