3.11–3.12 Nanoparticles and Their Applications

A free GCSE Chemistry lesson for AQA (8462) from OBA School: the size of nanoparticles, surface area to volume ratio, their uses and possible risks, plus an introduction to smart materials. Watch the video, read the explanation and worked examples, then try the revision questions. You can work through the full lesson, with every video, practice quizzes and printable worksheets with mark schemes, in our free online course.

What you will learn

• Compare the size of nanoparticles with atoms, molecules, fine and coarse particles, using standard form
• Calculate surface area to volume ratios and explain why they matter for nanoparticles
• Explain why nanoparticles may have different properties from the same material in bulk
• Describe uses of nanoparticles and evaluate their benefits and risks

Key words

• Nanoscience: The study of structures that are 1–100 nm in size, roughly a few hundred atoms.
• Nanometre (nm): 1 nm = 1 × 10⁻⁹ m, one billionth of a metre.
• Nanoparticle: A particle 1–100 nm across.
• Fine particles (PM2.5): Particles 100–2500 nm across (1 × 10⁻⁷ m to 2.5 × 10⁻⁶ m), e.g. soot.
• Coarse particles (PM10): Particles 2.5–10 µm across (2.5 × 10⁻⁶ m to 1 × 10⁻⁵ m), often called dust.
• Bulk material: A normal-sized piece of a material, much bigger than a nanoparticle.

How small is a nanoparticle?

Atoms are about 0.1 nm (1 × 10⁻¹⁰ m) across and small molecules are about 0.1–1 nm. A nanoparticle is 1–100 nm across, so it contains only a few hundred atoms.

Worked example: comparing sizes

A nanoparticle is 40 nm across. A human hair is 80 µm wide.
80 µm = 80 × 1000 nm = 80 000 nm
80 000 ÷ 40 = 2000

Answer: the hair is 2000 times wider

Each power of ten is one order of magnitude. The finest dust particles are about 100 nm across and the smallest nanoparticles about 1 nm, so nanoparticles can be two orders of magnitude (10² = 100 times) smaller than the finest dust. Nanoparticles are too small to be seen with a light microscope.

Maths: 1 m = 10³ mm = 10⁶ µm = 10⁹ nm. Write 40 nm in metres as 40 × 10⁻⁹ m = 4 × 10⁻⁸ m.

Surface area to volume ratio

For a cube of side L: surface area = 6 × L², volume = L³, so surface area : volume = 6 ÷ L.

Worked example: SA : V ratio

Cube of side 10 nm: SA = 6 × 10² = 600 nm²; V = 10³ = 1000 nm³; SA : V = 600 ÷ 1000 = 0.6 per nm
Cube of side 1 nm: SA = 6 nm²; V = 1 nm³; SA : V = 6 per nm

Answer: side 10 times smaller → SA : V 10 times bigger

Key fact: As the side of a cube decreases by a factor of 10, the surface area to volume ratio increases by a factor of 10.

Nanoparticles have a huge surface area to volume ratio, so a large fraction of their atoms are on the surface. This means they can have different properties from the same material in bulk. For example, nanoparticles make very good catalysts, so smaller amounts of material are needed.

Uses of nanoparticles

• sun creams; How nanoparticles help titanium dioxide or zinc oxide nanoparticles block harmful UV light and give better skin coverage, without leaving white marks
• catalysts; How nanoparticles help large surface area to volume ratio, so less material is needed (useful for expensive metals such as platinum)
• medicine; How nanoparticles help drug delivery to targeted cells; new diagnostic tests
• fabrics, wound dressings and deodorants; How nanoparticles help silver nanoparticles are antibacterial
• electronics and materials; How nanoparticles help tiny conducting wires and components; stronger, lighter composites (e.g. nanotubes)
• cosmetics; How nanoparticles help improve moisturisers and make-up without a greasy feel
• self-cleaning glass; How nanoparticles help a coating of titanium dioxide nanoparticles uses sunlight to break down dirt, which rain then washes away
• sensors and nanowires; How nanoparticles help carbon nanotubes can detect tiny amounts of a gas and form very small circuits for faster computers

Possible risks

Nanoparticles are so small that they might be breathed in, absorbed through the skin or pass into cells. They might also catalyse harmful reactions in the body or in the environment. Because they are new, their long-term effects are not yet fully known, and more research is needed.

• health: tiny particles breathed in could damage the lungs or pass into the blood; particles in cosmetics might be absorbed through the skin
• environment: silver nanoparticles washed out of clothes could reach rivers and build up in water organisms over time
• fire and explosion: a large mass of a nanoparticle catalyst powder has a huge surface area, so a spark could set off a very fast, violent reaction

Exam tip: In an “evaluate” question give benefits and risks, then a justified conclusion, e.g. “the benefits of better UV protection outweigh the risks, but more long-term research is needed”.

Extension: smart materials

Smart materials change one of their properties when their surroundings change. They are not part of the AQA specification, but you may meet them in your course:

• shape memory alloys (e.g. nitinol, nickel and titanium) return to their original shape when warmed: used in glasses frames and dental braces
• thermochromic pigments change colour with temperature: used in colour-change mugs and temperature strips
• photochromic materials change colour in bright light: used in lenses that darken in sunlight

Common mistakes

• Mixing up units: 1 µm = 1000 nm, not 100 nm. 1 nm = 10⁻⁹ m, not 10⁻⁶ m.
• Saying nanoparticles have a smaller surface area so they react more. They have a larger surface area to volume ratio.
• Thinking a factor of 10 smaller in side makes SA : V 100 or 1000 times larger. It is 10 times larger.
• Only giving benefits in an evaluation. Include risks and a conclusion.

Revision questions

Try these, then check your answers below each one.

Question 1. What is the size range of nanoparticles? (Choose from: 0.01–0.1 nm, 1–100 nm, 2500–10 000 nm, 100–2500 nm.)

Answer: 1–100 nm

Working: Nanoparticles are 1–100 nm across. Fine particles (PM2.5) are 100–2500 nm and coarse particles (PM10) are 2500–10 000 nm.

Question 2. True or false? If the side of a cube decreases by a factor of 10, its surface area to volume ratio increases by a factor of 10.

Answer: True

Working: True. SA : V = 6 ÷ L, so dividing L by 10 multiplies the ratio by 10.

Question 3. A coarse dust particle is 10 µm across. A nanoparticle is 20 nm across. How many times wider is the dust particle? (1 µm = 1000 nm)

Answer: 500

Working: 10 µm = 10 000 nm. 10 000 ÷ 20 = 500 times wider.

Related lessons

• Previous lesson: 3.9–3.10 Bonding in Metals and Giant Metallic Structures
• Next lesson: 4.1 Relative Masses and Moles
• In this chapter: 3.1 States of Matter
• In this chapter: 3.2 Atoms and Ions
• In this chapter: 3.3 Ionic Bonding

Continue in the full course

This lesson is section 3.11–3.12 (AGCCH0311) of our free GCSE Chemistry course for AQA. In the full course you get every video for this section, a self-marking practice quiz, a printable worksheet with a mark scheme, chapter tests, and your progress saved. Go to the full GCSE Chemistry course.