A nanoparticle has at least one dimension between 1 and 100 nanometres (1-100 nm). Free GCSE AQA Chemistry notes with key terms and 13 questions answered.
Updated 19 Mar 2026 · Revise Right Team
Particle Size Categories and Scale is part of Bulk and surface properties of matter including nanoparticles (chemistry only) in GCSE AQA Higher Chemistry.
4 min
Reading time
24
Lessons in this topic
GCSE AQA Higher
Pathway
Reviewed by Revise Right
Content review
What this lesson covers
A nanoparticle has at least one dimension between 1 and 100 nanometres (1-100 nm). Free GCSE AQA Chemistry notes with key terms and 13 questions answered.
Compare the sizes of nanoparticles, fine particles, and coarse particles using scientific notation
Explain what nanoscience is and why particle size matters at the nanoscale
Calculate particle sizes in different units and convert between metres and nanometres
Evaluate the scale of nanoparticles compared to atoms and molecules
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Use this lesson to stay inside Bulk and surface properties of matter including nanoparticles (chemistry only) while connecting the detail back to the wider Topic 2: Bonding, structure, and the properties of matter topic.
Topic 2: Bonding, structure, and the properties of matter
Bulk and surface properties of matter including nanoparticles (chemistry only)
GCSE AQA Higher Chemistry
Revision notes
Read the core explanations from Particle Size Categories and Scale before testing yourself from memory.
1. The Invisible World Around Us
Right now, you're breathing in particles so small that millions could fit on the full stop at the end of this sentence. These aren't just tiny bits of dust - they're engineered materials that behave completely differently from their larger cousins. Welcome to the world of particle size categories, where being small isn't just about fitting through gaps - it's about having superpowers.
Understanding particle sizes matters because the smaller something gets, the more its surface area dominates its behaviour. This is why nanoparticles can conduct electricity differently, why they're used in sunscreen, and why they're revolutionising medicine.
2. The Three Size Categories
Notice the pattern here - the particle-size categories increase by different factors, so it is better to compare the actual boundary values than assume a fixed 10-fold change. Nanoparticles are measured in nanometres, fine particles in hundreds of nanometres, and coarse particles in micrometres. This isn't random - it reflects how particles behave differently at each scale.
3. Making Sense of the Numbers
The sizes we're dealing with are almost impossible to visualise. A nanometre is one billionth of a metre (1 × 10⁻⁹ m). To put this in perspective, if a marble were scaled up to the size of Earth, a nanometre would be about the size of that original marble.
Worked example: Converting Between Units
Convert 2500 nm to metres and express in standard form
1 nm = 1 × 10⁻⁹ m — Nano means one billionth
2500 nm × (1 × 10⁻⁹ m/nm) — Multiply by the conversion factor
2500 × 10⁻⁹ m = 2.5 × 10³ × 10⁻⁹ m — Express 2500 in standard form first
2.5 × 10³⁻⁹ m = 2.5 × 10⁻⁶ m — Add the indices: 3 + (-9) = -6
Answer: 2.5 × 10⁻⁶ m
This calculation shows us that 2500 nm equals 2.5 micrometres - exactly the boundary between fine and coarse particles. The PM2.5 and PM10 labels make more sense now - they refer to the maximum particle diametre in micrometres.
4. Comparing Particles to Atoms and Molecules
Atoms are roughly 0.1-0.3 nm in diametre. This means the smallest nanoparticles (1 nm) contain only a few atoms arranged in a cluster. Large nanoparticles can contain many thousands of atoms arranged in a structure, but the exact number depends on the material and particle size.
Simple molecules like water (H₂O) are about 0.3 nm across. Complex biological molecules like proteins can be 2-10 nm. This puts them right at the boundary between individual molecules and nanoparticles - which is why some large proteins are considered biological nanoparticles.
5. Why Size Categories Matter
These size categories aren't just academic - they have real-world consequences. Coarse particles get trapped in your nose and throat. Fine particles can reach your lungs. But nanoparticles? They can cross into your bloodstream and even reach your brain.
The behaviour changes because as particles get smaller, their surface area to volume ratio increases dramatically. A 10 nm nanoparticle has a much higher proportion of its atoms on the surface compared to a 10 μm coarse particle. Surface atoms behave differently - they're more reactive, more likely to interact with other substances.
6. Exam Technique and Common Mistakes
Exam questions on particle sizes often test your ability to convert between units and compare scales. The key is getting comfortable with powers of 10 and scientific notation.
Watch out for unit conversion errors - the most common mistake is forgetting that 1 μm = 1000 nm. Also, don't assume smaller always means less dangerous - nanoparticles can be more reactive precisely because they're smaller.
Exam precision note: In Particle Size Categories and Scale - Sizes of particles and their properties - Bulk and surface properties of matter including nanoparticles (chemistry only), always identify the key chemical idea first, then link it to evidence, data, or an equation. A high-scoring GCSE answer names the particles involved, states what changes, and justifies the conclusion using correct scientific language. Where calculations are used, show each step with units and keep significant figures sensible. Finally, check that terminology matches AQA wording so your answer is unambiguous and mark-scheme friendly.
Nanoparticles are between 1 and 100 nm in size, but that range still covers a wide spread of particle sizes. The phrase “a few hundred atoms” is best treated as a rough description of the very smallest nanoparticles. As particles get larger within the nanoscale, they contain far more atoms, so students should focus on the size range first and avoid treating one atom-count estimate as applying to the whole range.
Sources and content standards
Published by Revise Right. Use the official specification reference to check the requirements for your course. Content updated: 2026-03-19.
There are 1000 nanometres in a micrometre, so 1 μm = 1000 nm. Forgetting this is the most common unit conversion error with particle sizes; for example, 2500 nm is 2.5 micrometres, the boundary between fine and coarse particles.
What size is a nanoparticle?
A nanoparticle has at least one dimension between 1 and 100 nanometres (1-100 nm). A nanometre is one billionth of a metre, or 1 × 10⁻⁹ m.
How many atoms are in a nanoparticle?
The number of atoms in a nanoparticle depends on its size and material. The smallest nanoparticles (1 nm) contain only a few atoms, a few hundred atoms is a rough description of very small ones, and large nanoparticles can contain many thousands of atoms.
What are fine particles?
Fine particles (PM2.5) are particles with diametres between 100 and 2500 nm (1 × 10⁻⁷ m to 2.5 × 10⁻⁶ m). The 2.5 refers to 2.5 micrometres, the upper size limit, and fine particles can reach the lungs.
How big is a nanoparticle compared to an atom?
Atoms are roughly 0.1-0.3 nm across, so the smallest nanoparticles, at 1 nm, contain only a few atoms arranged in a cluster. Simple molecules such as water are about 0.3 nm across, while large nanoparticles can contain many thousands of atoms.
What are coarse particles?
Coarse particles (PM10) are particles with diametres between 2.5 and 10 micrometres (2.5 × 10⁻⁶ m to 1 × 10⁻⁵ m). They are often called dust and include pollen, mould spores and larger pollution particles.
What is the difference between PM2.5 and PM10?
PM2.5 are fine particles between 100 and 2500 nm across, while PM10 are coarse particles between 2.5 and 10 micrometres across, often called dust. The numbers refer to the maximum particle size in micrometres.
How do you convert nanometres to metres?
To convert nanometres to metres, multiply by 1 × 10⁻⁹, because 1 nm = 1 × 10⁻⁹ m. For example, 2500 nm = 2.5 × 10³ × 10⁻⁹ m = 2.5 × 10⁻⁶ m, which is 2.5 micrometres.
What does PM2.5 mean?
PM2.5 is the label for fine particles, and the 2.5 refers to 2.5 micrometres, the maximum particle diametre. In the same way, PM10 refers to coarse particles up to 10 micrometres across.
What is a nanometre?
A nanometre is one billionth of a metre: 1 nm = 1 × 10⁻⁹ m. Nanoparticles are measured in nanometres, fine particles in hundreds of nanometres and coarse particles in micrometres, where 1 μm = 1000 nm.
How big is an atom in nanometres?
Atoms are roughly 0.1-0.3 nm in diametre. This means the smallest nanoparticles, at 1 nm, contain only a few atoms arranged in a cluster, while a simple molecule like water is about 0.3 nm across.
Where do different sized particles go in the body?
Coarse particles get trapped in the nose and throat, fine particles can reach the lungs, and nanoparticles can cross into the bloodstream and even reach the brain. Smaller particles also have a higher surface area to volume ratio, so they are more reactive.
Are proteins nanoparticles?
Some large proteins are considered biological nanoparticles. Complex biological molecules like proteins can be 2-10 nm across, which puts them right at the boundary between individual molecules and nanoparticles, which are 1-100 nm.