Nanoparticles and Why Surface Area Changes Everything · seed 1 · A4, ink-friendly. The answer key prints on its own page for grown-ups.

Small enough to turn into something new

Science · Matter & Materials · ages 15-16
Name ______________________   Date ____________

  1. Why does a nanoparticle behave differently from a lump of the same substance?

    • It holds a new kind of atom
    • Almost every atom sits on the surface, ready to react
    • It has lost all of its surface

  2. What size of particle counts as a nanoparticle?

    • Between 1 and 100 nanometres across
    • Between 1 and 100 millimetres across
    • Between 1 and 100 centimetres across

  3. Safety data for a bulk substance always applies to its nanoparticles.

    Circle one:   True   False

  4. A 2 cm cube is cut into eight 1 cm cubes. The surface doubles from 24 to 48 while the stuff stays the same. What happens to surface reaction speed?

    • It stays about the same
    • It roughly doubles
    • It drops by half

  5. A 3 cm cube has surface 54 and volume 27. It is sliced into twenty seven 1 cm cubes with total surface 162 and the same volume 27. What is the new surface area to volume ratio?

    Answer: ______________

  6. A 2 cm cube has surface area 24 and a surface area to volume ratio of 3 per cm. What is its volume?

    Answer: ______________

  7. Bulk titanium dioxide is safe, yet its nanoparticle form in sunscreen still needs testing. Why?

    • Nanoparticles wash off faster in rain
    • Testing is only done for marketing reasons
    • The nano form can slip into cells and lungs like a gas

  8. A student says gold nanoparticles glow red because they contain a new element. What is wrong?

    • Gold cannot form particles that small
    • The colour comes from geometry, since surface atoms dominate
    • Red light cannot come from any metal
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Answer key

For grown-ups. Fold this page away before handing over the rest.

Small enough to turn into something new W1-mt_pTG4U3Hvdn-s1

  1. Almost every atom sits on the surface, ready to react · Surface atoms dominate at the nanoscale, so surface properties run the show.
  2. Between 1 and 100 nanometres across · Nano means the 1 to 100 nanometre band where surface effects take over.
  3. False · Nanoparticles can enter cells and lungs, so they need their own harm tests.
  4. It roughly doubles · Surface reactions scale with surface, so twice the surface means roughly twice the speed.
  5. 6 · Divide the new surface 162 by the volume 27 to get 6 per cm.
  6. 8 · Surface 24 divided by ratio 3 gives volume 8.
  7. The nano form can slip into cells and lungs like a gas · The new size opens a new route into the body that bulk lumps lack.
  8. The colour comes from geometry, since surface atoms dominate · The chemistry is still gold, while the geometry is new.
Worksheet · LightMySky