AQA GCSE Chemistry Foundation (8462), Foundation tier · Bonding, structure and the properties of matter › Nanoparticles
Practise Sizes of particles and their properties. 9 exam-style questions plus unlimited generated ones on this subtopic, at up to four difficulty levels, with full mark schemes and a progress tracker. Free, no account needed.
What nanoparticles are, how their size compares with atoms, fine particles and coarse particles, and why their very high surface area to volume ratio gives them different properties. Expect size comparisons in standard form and surface area to volume calculations for cubes. Nanoscience is in GCSE Chemistry only, not in Combined Science.
Key facts
Nanoparticles: 1–100 nm across (a few hundred atoms)
1 nm = 1 × 10−9 m
Fine particles, PM2.5: 100–2500 nm (1 × 10−7 m to 2.5 × 10−6 m)
Coarse particles, PM10 (dust): 2.5 × 10−6 m to 1 × 10−5 m
Radius of an atom ≈ 0.1 nm = 1 × 10−10 m
Cube: surface area = 6L2, volume = L3, surface area ÷ volume = 6 ÷ L
Side 10 times smaller → surface area to volume ratio 10 times bigger
High surface area to volume ratio → different properties from bulk; smaller quantities needed
Notes
Nanoscience and particle sizes
diagram
Nanoscience is about structures that are 1 to 100 nm in size, containing roughly a few hundred atoms.
1 nanometre (nm) = 1 × 10−9 m (one billionth of a metre).
Nanoparticles are 1 to 100 nm across.
Fine particles (PM2.5) are 100 to 2500 nm across (1 × 10−7 m to 2.5 × 10−6 m).
Coarse particles (PM10) are 2.5 × 10−6 m to 1 × 10−5 m across (2500 to 10 000 nm). Coarse particles are often called dust.
An atom has a radius of about 0.1 nm (1 × 10−10 m), and a small molecule is usually less than 1 nm across. So a 10 nm nanoparticle is about 50 atoms across.
Nanoparticles are 1 to 100 nm: much bigger than atoms, much smaller than fine dust.
Surface area to volume ratio
diagram
For a cube with side L: surface area = 6 × L2 (six square faces), volume = L3, and surface area ÷ volume = 6 ÷ L.
Make the side 10 times smaller and the surface area to volume ratio gets 10 times bigger.
Side 10 nm: surface area 600 nm2, volume 1000 nm3, ratio 0.6 nm−1. Side 1 nm: surface area 6 nm2, volume 1 nm3, ratio 6 nm−1.
So when the side of a cube decreases by a factor of 10, the surface area to volume ratio increases by a factor of 10.
Nanoparticles are so small that a large fraction of their atoms are at the surface.
Why size changes properties
Because of their very high surface area to volume ratio, nanoparticles may have different properties from the same material in bulk (in large pieces).
For example, a metal that is unreactive in bulk can be a good catalyst as nanoparticles, because far more of its atoms are exposed at the surface.
It can also mean that smaller quantities of a nanoparticle material are needed to be effective than of the same material with normal-sized particles.
How to answer each type of question
Convert sizes and classify particles
2 to 3 marksGrade 5
Convert every size to the same unit, usually nm: multiply metres by 109.
Compare with the ranges: nano 1–100 nm, fine 100–2500 nm, coarse 2500–10 000 nm.
Take care with standard form: 10−7 m is bigger than 10−8 m.
Example. The table gives the diameters of three particles.
Particle
Diameter in m
P
4 × 10−8
Q
6 × 10−6
R
1.5 × 10−7
Classify each particle as a nanoparticle, a fine particle or a coarse particle.Show the model answerHide the model answer
P = 40 nm, so a nanoparticle (1) Q = 6000 nm, so a coarse particle (1) R = 150 nm, so a fine particle (1)
Don’t lose marks
Using the radius of an atom when you need its diameter, or the other way round. Read which one the question gives.
Getting standard form comparisons backwards: 1 × 10−9 m is smaller than 1 × 10−7 m.
Forgetting the 6 in the surface area of a cube, or using only one face.
Saying the ratio decreases as particles get smaller. Smaller particles have a larger surface area to volume ratio.
Writing 'nanoparticles have a large surface area'. Say 'a high surface area to volume ratio'.
More tips
Memory tricks
Size ladder in nm: atom about 0.1 (radius) → nanoparticle 1–100 → fine 100–2500 → coarse 2500–10 000.
PM2.5 and PM10 give the upper size in micrometres: 2.5 µm = 2500 nm and 10 µm = 10 000 nm.
Cube shortcut: surface area ÷ volume = 6 ÷ side. Use it to check your full working.
Metres to nm: add 9 to the power of ten, e.g. 4 × 10−8 m = 4 × 101 nm = 40 nm.
Exam technique
Show each step of a surface area to volume calculation: surface area, then volume, then the ratio. Each step can earn a mark.
Put all sizes in the same unit before you compare them.
When explaining why nanoparticles behave differently, always use the phrase 'surface area to volume ratio'.
What each grade needs
What you need to be able to do, from the first marks up to the top grade.
Grade 4
State the size range of nanoparticlesNanoparticles are 1 to 100 nm across and contain a few hundred atoms.
Grade 5
Convert between nanometres and metres1 nm = 1 × 10−9 m, so 50 nm = 5 × 10−8 m.
Grade 5
Classify particles as nano, fine or coarseNano 1–100 nm; fine (PM2.5) 100–2500 nm; coarse (PM10) 2500–10 000 nm.
Quick recall
Cover the answers and test yourself. The app has these as flashcards that come back just before you'd forget them.
Complete the sentence. Nanoparticles have a high .................... to volume ratio.
surface area
Sample questions
Written for this site in the style of AQA exam questions. They are not taken from real past papers.
Question 1Easy4 marks
Nanoscience is the study of very small structures, such as nanoparticles.
(a) What size are nanoparticles? Tick (✓) one box.[1]
1–100 nm
100–2500 nm
2500–10 000 nm
more than 1 mm
(b) What is 1 nm in metres? Tick (✓) one box.[1]
1 × 10−3 m
1 × 10−6 m
1 × 10−9 m
1 × 10−12 m
(c) Complete the sentence. Nanoparticles have a high .................... to volume ratio.[1]
(d) How do fine particles (PM2.5) compare in size with nanoparticles? Tick (✓) one box.[1]
They are larger.
They are smaller.
They are the same size.
They are single atoms.
Show the answer and mark scheme
(a)Answer: 1–100 nm
(b)Answer: 1 × 10−9 m
(c)Answer: surface area
surface area
(d)Answer: They are larger.
Question 2Medium6 marks
A nanoparticle is a cube with sides of length 20 nm.
(a) Calculate the surface area of the cube.[1]
(b) Calculate the volume of the cube.[1]
(c) Calculate the surface area to volume ratio of the cube.[1]
(d) The length of the side of a cube is decreased by a factor of 10. What happens to its surface area to volume ratio?[1]
(e) Explain why nanoparticles of a catalyst can be more effective than larger particles of the same catalyst.[2]
Show the answer and mark scheme
(a)Answer: 2400 nm2
(6 × 20 × 20 =) 2400 (nm2)
(b)Answer: 8000 nm3
(20 × 20 × 20 =) 8000 (nm3)
(c)Answer: 0.3 nm−1 (0.3 : 1)
(2400 ÷ 8000 =) 0.3 (nm−1)
(d)Answer: It increases by a factor of 10.
it increases by a factor of 10 / becomes 10 times larger
(e)Answer: They have a much larger surface area to volume ratio, so more of the catalyst is exposed and smaller quantities are needed.
nanoparticles have a larger surface area to volume ratio / more of their atoms are at the surface
so smaller quantities are needed / more reacting particles can collide with the surface at once