Nanoparticles [H]

This is a Higher Tier only lesson covering nanoparticles and nanoscience, as required by the AQA GCSE Chemistry specification (4.2.2). Nanoparticles are structures between 1 and 100 nanometres in size. You need to understand how their properties differ from bulk materials, how to calculate surface area to volume ratios, and the applications and risks of nanoparticles.

---

What Are Nanoparticles?

Nanoparticles are particles that have dimensions between 1 nm and 100 nm (nanometres). A nanometre (nm) is one billionth of a metre:

1 nm = 1 x 10^-9 m

To put this in perspective:

Object	Approximate Size
Width of a human hair	80,000 nm
Red blood cell	7,000 nm
Virus	20-300 nm
Nanoparticle	1-100 nm
Water molecule	0.275 nm

Nanoscience is the study of structures and materials at the nanoscale (1-100 nm). At this scale, materials can have very different properties compared to the same materials in bulk (large-scale) form.

Exam Tip: [H] The size range for nanoparticles is 1-100 nm. If a particle is larger than 100 nm, it is NOT a nanoparticle. If a particle is smaller than 1 nm, it is at the atomic/molecular scale. This definition is important — learn the exact range.

---

Comparing Particle Sizes

The AQA specification distinguishes between three scales of particle:

Type	Size Range	Examples
Coarse particles (dust)	PM10: 1 x 10^-5 m to 2.5 x 10^-6 m	Pollen, dust, soot
Fine particles	PM2.5: less than 2.5 x 10^-6 m	Combustion products, industrial emissions
Nanoparticles	1 x 10^-9 m to 1 x 10^-7 m (1-100 nm)	Engineered nanoparticles, quantum dots

Nanoparticles typically contain only a few hundred to a few thousand atoms, compared to billions in bulk materials.

---

Surface Area to Volume Ratio

The most important feature of nanoparticles is their very high surface area to volume ratio. As particles get smaller, the proportion of atoms on the surface increases dramatically.

Why Does This Matter?

When particles are very small:

• A greater proportion of atoms are on the surface.
• Surface atoms interact more directly with other substances.
• This makes nanoparticles more reactive than the same material in bulk form.
• It also changes their physical properties (e.g. colour, melting point, magnetic behaviour).

Calculating Surface Area to Volume Ratio

For a cube with side length a:

• Surface area = 6a^2
• Volume = a^3
• SA:V ratio = 6a^2 / a^3 = 6/a

Side Length	Surface Area	Volume	SA:V Ratio
1 cm	6 cm^2	1 cm^3	6:1
1 mm (0.1 cm)	0.06 cm^2	0.001 cm^3	60:1
1 nm	6 nm^2	1 nm^3	6,000,000:1

As the particle gets smaller, the surface area to volume ratio increases dramatically. This is why nanoparticles have such different properties.

graph TD
    A["Nanoparticles<br/>1-100 nm"] --> B["Very High Surface Area<br/>to Volume Ratio"]
    B --> C["More atoms on<br/>the surface"]
    C --> D["Different Properties<br/>from Bulk Material"]
    D --> E["Different Colour"]
    D --> F["Higher Reactivity"]
    D --> G["Different Melting Point"]
    D --> H["Different Magnetic<br/>Properties"]
    D --> I["Different Electrical<br/>Properties"]

    style A fill:#8e44ad,color:#fff
    style B fill:#e74c3c,color:#fff
    style D fill:#2c3e50,color:#fff

Exam Tip: [H] You may be asked to calculate the surface area to volume ratio for a given shape (usually a cube or a sphere). For a cube: SA = 6 x side^2, V = side^3. For a sphere: SA = 4 x pi x r^2, V = (4/3) x pi x r^3. Always show your working clearly and give the final ratio in its simplest form.

---

Properties of Nanoparticles

Because of their high surface area to volume ratio, nanoparticles have properties that differ from bulk materials:

Property	Bulk Material	Nanoparticle Form
Colour	Gold is gold/yellow	Gold nanoparticles can appear red, blue, or purple depending on size
Reactivity	Lower (less surface area exposed)	Higher (more surface atoms available for reactions)
Melting point	Higher	Lower (surface atoms have fewer bonds)
Catalytic activity	Standard	Enhanced (more surface sites for reactions)
Electrical properties	Standard conductor	Can become semiconductors or have quantum effects
Magnetic properties	Standard	Can become superparamagnetic

---

Applications of Nanoparticles

Nanoparticles have many current and potential applications:

In Medicine

Application	How Nanoparticles Are Used
Drug delivery	Nanoparticles (e.g. fullerenes, liposomes) can carry drug molecules directly to diseased cells, reducing side effects on healthy tissue.
Imaging	Quantum dots (semiconductor nanoparticles) can be used as fluorescent markers to image tumours and track biological processes.
Antibacterial	Silver nanoparticles have antibacterial properties and are used in wound dressings, surgical instruments, and coatings.
Sunscreens	Zinc oxide and titanium dioxide nanoparticles absorb UV radiation effectively while appearing transparent on skin.

In Technology

Application	How Nanoparticles Are Used
Electronics	Nanotubes and graphene used in smaller, faster electronic components.
Catalysts	High surface area = more active catalytic sites, making reactions faster and more efficient.
Coatings	Self-cleaning glass, scratch-resistant coatings, anti-fingerprint screens.
Energy	Improving efficiency of solar cells and batteries.

In Materials

Application	How Nanoparticles Are Used
Composites	Adding nanoparticles to materials makes them stronger and lighter (e.g. carbon nanotubes in sports equipment).
Textiles	Silver nanoparticles in fabrics provide antibacterial and odour-resistant properties.
Paints	Nanoparticle pigments provide better coverage and durability.