C8: Nanoscience
Nanoparticles and their uses (Higher Tier only)
C8 Nanoscience
📋 Key Definitions
Nanoparticle: A particle that has a size between 1 nm and 100 nm (1 × 10⁻⁹ m to 100 × 10⁻⁹ m). Nanoparticles are typically a few hundred atoms in size.
Nanoscience: The study of structures that are 1-100 nm in size. It involves studying and working with materials on an extremely small scale.
Surface area to volume ratio (SA:V): The ratio of the surface area of a particle to its volume. As particles get smaller, their surface area to volume ratio increases dramatically.
📏 Particle Size Categories
| Particle Type | Size Range | Examples |
|---|---|---|
| Coarse particles (dust) | Greater than 2500 nm (2.5 μm) | Dust, pollen, fine sand |
| Fine particles | 100 nm to 2500 nm (0.1-2.5 μm) | PM2.5 air pollution particles |
| Nanoparticles | 1 nm to 100 nm | Nanoparticle silver, titanium dioxide nanoparticles |
1 nanometre (1 nm) = 1 × 10⁻⁹ m = 0.000000001 m. A nanoparticle is roughly the same size as a few hundred atoms. Nanoparticles are much smaller than fine particles and coarse particles.
📐 Surface Area to Volume Ratio
As particles get smaller, their surface area to volume ratio increases. This is because volume decreases faster than surface area when a particle shrinks. A higher SA:V ratio means a greater proportion of atoms are on the surface, making nanoparticles much more reactive than the same material in bulk form.
Surface area to volume ratio = surface area ÷ volume
Worked Example - Calculating SA:V Ratio for Cubes
Calculate the SA:V ratio for cubes of side length: (a) 10 cm, (b) 1 cm, (c) 0.1 cm
(a) Side = 10 cm: Surface area = 6 × 10² = 600 cm². Volume = 10³ = 1000 cm³. SA:V = 600/1000 = 0.6:1
(b) Side = 1 cm: Surface area = 6 × 1² = 6 cm². Volume = 1³ = 1 cm³. SA:V = 6/1 = 6:1
(c) Side = 0.1 cm: Surface area = 6 × 0.1² = 0.06 cm². Volume = 0.1³ = 0.001 cm³. SA:V = 0.06/0.001 = 60:1
As the cube gets 10× smaller, the SA:V ratio gets 10× larger. This shows why nanoparticles have a much higher SA:V ratio than bulk materials.
Worked Example - Comparing SA:V Ratios
A cube of side 2 nm is divided into 8 cubes of side 1 nm. Compare the total surface area and SA:V ratio before and after division.
Before (one 2 nm cube): SA = 6 × 2² = 24 nm². Volume = 2³ = 8 nm³. SA:V = 24/8 = 3:1
After (eight 1 nm cubes): Each small cube: SA = 6 × 1² = 6 nm². Total SA = 8 × 6 = 48 nm². Total volume = 8 × 1 = 8 nm³ (same). SA:V = 48/8 = 6:1
The total volume stays the same but the total surface area doubles. The SA:V ratio has doubled from 3:1 to 6:1.
Why SA:V ratio matters: Nanoparticles have a very high surface area to volume ratio compared to bulk materials. This means a much larger fraction of the atoms are on the surface, making nanoparticles much more chemically reactive than the same substance in bulk form. This is why nanoparticle catalysts are very effective.
🧪 Uses of Nanoparticles
Nanoparticles have unusual properties because of their high surface area to volume ratio. These properties make them useful in many applications.
| Use | How nanoparticles help |
|---|---|
| Medicine delivery | Nanoparticles can carry drugs to specific cells, reducing side effects and improving effectiveness |
| Sunscreens | Titanium dioxide (TiO₂) nanoparticles block UV light effectively while being colourless on the skin |
| Catalysts | High SA:V ratio means more surface available for reactions, making nanoparticle catalysts very efficient |
| Electronics | Nanoparticles can be used to make smaller, faster and more efficient electronic components |
| Coatings | Self-cleaning windows and anti-bacterial coatings use nanoparticles |
| Sensors | Nanoparticle sensors can detect very small amounts of substances |
Examples of Nanoparticle Uses
- Silver nanoparticles: Added to clothing, plasters and wound dressings for their antibacterial properties
- Titanium dioxide nanoparticles: Used in sunscreens to absorb UV radiation - they are more effective and less visible on skin than larger particles
- Gold nanoparticles: Used in pregnancy tests and cancer treatments to target specific cells
- Carbon nanotubes: Used to make strong, lightweight materials for sports equipment and electronics
⚠️ Risks of Nanoparticles
Risks of nanoparticles: Because nanoparticles are so small, they can be absorbed into the body and into cells. The long-term health effects of exposure to nanoparticles are not fully understood. Nanoparticles could be toxic or cause harm in ways that larger particles of the same substance do not.
- Nanoparticles are so small they can be inhaled and pass into the bloodstream or cells
- They may be toxic in ways that larger particles of the same substance are not
- Their high reactivity could cause unexpected chemical reactions in the body
- Long-term effects on health and the environment are unknown
- It is difficult to study nanoparticle effects because they are so small
- Nanoparticles in sunscreens could be absorbed through the skin - the long-term effects are uncertain
Worked Example - Evaluating Nanoparticle Use
Titanium dioxide nanoparticles are used in sunscreens instead of larger TiO₂ particles. Suggest one advantage and one concern.
Advantage: Nanoparticles of TiO₂ are colourless and invisible on the skin (unlike larger particles which leave a white residue), and they absorb UV radiation effectively to protect the skin.
Concern: The nanoparticles are so small they could be absorbed through the skin into the body. The long-term health effects of this absorption are unknown, and they could potentially be toxic.
Worked Example - Why Nanoparticles Are More Reactive
Explain why nanoparticle silver is a more effective antibacterial agent than bulk silver.
Nanoparticles have a much higher surface area to volume ratio than bulk silver. This means a much larger proportion of the silver atoms are on the surface and available to interact with bacteria. The high SA:V ratio makes nanoparticle silver much more chemically reactive, so it can kill bacteria more effectively even in very small quantities.
❓ Practice Questions
Q1: Higher Define the term nanoparticle and state the size range in nanometres and in metres.
Q2: Higher A cube has a side length of 5 nm. Calculate its surface area, volume and surface area to volume ratio.
Q3: Higher Explain why nanoparticles are often much more reactive than the same substance in bulk form.
Q4: Higher Give two uses of nanoparticles and explain why nanoparticles are useful in each case. Suggest one risk of using nanoparticles.
Q5: Higher A cube of side 4 cm is cut into 64 cubes of side 1 cm. Calculate the total surface area and SA:V ratio before and after. Explain the significance of this change.
✅ Answers
- A nanoparticle is a particle with a size between 1 nm and 100 nm. In metres: 1 × 10⁻⁹ m to 100 × 10⁻⁹ m (1 nm to 100 nm). Nanoparticles are typically made up of a few hundred atoms.
- Surface area = 6 × 5² = 6 × 25 = 150 nm². Volume = 5³ = 125 nm³. SA:V ratio = 150 ÷ 125 = 1.2:1.
- Nanoparticles have a much higher surface area to volume ratio than bulk materials. This means a much larger proportion of the atoms are on the surface of the particle and are available to react. With more surface atoms exposed, the rate of reaction is much faster, making nanoparticles much more reactive.
- Use 1: Sunscreens - titanium dioxide nanoparticles absorb UV radiation effectively and are invisible on the skin (no white residue). Use 2: Medicine delivery - nanoparticles can carry drugs directly to specific cells, reducing side effects. Risk: Nanoparticles are so small they could be absorbed into the body through the skin or by inhalation. The long-term health effects are not fully understood and they could be toxic.
- Before: SA = 6 × 4² = 96 cm². Volume = 4³ = 64 cm³. SA:V = 96/64 = 1.5:1. After: Each small cube SA = 6 × 1² = 6 cm². Total SA = 64 × 6 = 384 cm². Volume = 64 × 1 = 64 cm³ (same). SA:V = 384/64 = 6:1. Significance: The total surface area has increased from 96 to 384 cm² (4 times greater) while the volume stays the same. The SA:V ratio has increased from 1.5:1 to 6:1. This shows why smaller particles (like nanoparticles) have a much higher SA:V ratio, making them more reactive and useful as catalysts.
🎯 Exam Tips
- This is Higher Tier only - it will not appear on Foundation papers
- SA:V calculations: for a cube, SA = 6 × side² and volume = side³. Always show your working
- When asked why nanoparticles are more reactive, always mention "high surface area to volume ratio" AND "more atoms on the surface available to react"
- For evaluation questions about nanoparticle uses, always give both an advantage AND a concern/risk
- Remember the size ranges: coarse > 2500 nm, fine 100-2500 nm, nano 1-100 nm
- 1 nm = 1 × 10⁻⁹ m - be confident converting between nanometres and metres
- Common mistake: saying nanoparticles are "safer" - they could actually be more dangerous because they can enter cells
🔢 Maths Skills
Mathematical Skills
Surface area to volume ratio: For a cube, SA = 6 × side² and V = side³. SA:V = 6/side. As side length decreases, SA:V increases.
Example: A 2 nm cube: SA = 24 nm², V = 8 nm³, SA:V = 3:1. Eight 1 nm cubes (same total volume): SA = 48 nm², SA:V = 6:1. The SA:V doubles when the particle size halves.
⚠️ Common Misconceptions
Watch Out!
Nanoparticles have the same properties as the bulk material. Wrong: nanoparticles have same properties as bulk Correct: nanoparticles have different properties due to their much higher surface area to volume ratio, which makes them more reactive
Nanoparticles are always safe because they are used in products like sunscreens. Wrong: nanoparticles are always safe Correct: nanoparticles may have unforeseen risks because they can enter cells and their long-term health effects are not fully understood
✍️ 6-Mark Question
Extended Answer
6 marks: Evaluate the uses and risks of nanoparticles.
Nanoparticles have a very high surface area to volume ratio, making them much more reactive than bulk materials. This makes them useful as catalysts (more surface available for reactions), in medicine (carrying drugs to specific cells), and in sunscreens (TiO₂ nanoparticles absorb UV effectively and are invisible on skin). However, there are risks: nanoparticles are so small they can be inhaled deep into the lungs and pass into cells or the bloodstream. Their high reactivity could cause unexpected chemical reactions in the body. The long-term health and environmental effects are not fully understood. It is therefore important that nanoparticles are thoroughly tested before widespread use.
Mark scheme: 1 mark for high SA:V explanation; 1 mark for a valid use with explanation; 1 mark for a second use with explanation; 1 mark for a risk (absorption into body); 1 mark for a second risk (unknown long-term effects); 1 mark for balanced evaluation.
📊 AO3: Analyse & Evaluate
Analysis and Evaluation
The table shows SA:V data for catalyst particles of different sizes:
| Particle size (nm) | SA:V ratio | Reaction rate (g/s) |
|---|---|---|
| 100 | 0.06:1 | 0.8 |
| 10 | 0.6:1 | 7.5 |
| 1 | 6:1 | 72 |
Question: Describe the relationship between particle size and reaction rate. Explain this relationship. Suggest why 1 nm particles might not be chosen for an industrial process despite being fastest.
Answer: As particle size decreases, SA:V ratio increases and reaction rate increases rapidly (approximately tenfold for each tenfold size decrease). This is because a higher proportion of atoms are on the surface and available to react. Despite being fastest, 1 nm particles might not be chosen because they could be difficult to handle, may pose health risks to workers, could be too expensive to produce, or might be unstable and clump together.
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