AQA · GCSE · Chemistry
Course version: 8462 · Version from Sept 2018
Nanoparticles may have properties different from those for the same…
Full specification wording
Sizes of particles and their properties: Nanoparticles may have properties different from those for the same materials in bulk because of their high surface area to volume ratio.
Nanoparticles have a very large surface area compared with their volume, so a high proportion of their atoms are at the surface.
Checked against the AQA 8462 specification (opens in a new tab) on .
- Point 4 of 6
Study notes
From the checked teaching notes for this specification point.
The idea
Nanoparticles have a very large surface area compared with their volume, so a high proportion of their atoms are at the surface. These surface atoms have fewer neighbours and different bonding environments from atoms inside a bulk solid, which can change melting point, reactivity, electrical conductivity, colour and catalytic activity. For example, gold is unreactive and yellow in bulk, but gold nanoparticles can appear red or purple and can act as catalysts. Titanium dioxide nanoparticles are effective in sunscreens because they absorb ultraviolet radiation while being transparent on the skin.
What earns the marks
- States that nanoparticles have a high surface area to volume ratio.
- Explains that a high proportion of atoms in a nanoparticle are at the surface.
- Links surface atoms with different bonding or coordination to altered physical and chemical properties.
- Gives a valid example, such as gold nanoparticles having a different colour or catalytic activity from bulk gold.
- Uses the surface area to volume ratio to explain why nanoscale properties differ from bulk properties.
Common mistakes and how to put them right
Claiming nanoparticles are a different chemical element from the bulk material.
Put it right by stating they are the same material with different particle size and surface effects.
Saying nanoparticles have a high surface area to volume ratio because they are small, without explaining that a greater fraction of atoms are at the surface.
Put it right: Explicitly linking the ratio to surface atom proportion.
Assuming all properties change in the same way for every material.
Put it right by giving specific examples and noting that the effect depends on the material and property.
Exam tips
- Always name the property that changes, such as colour, melting point or catalytic activity, and link it to the high surface area to volume ratio.
- Use a named example, such as gold nanoparticles or titanium dioxide in sunscreen, to support the explanation.
- Avoid saying nanoparticles are a new element; emphasise that the bulk material and nanoparticles have the same chemical identity.
Try the lesson
The start of the Sizes of particles and their properties: Nanoparticles may have properties different from those for the same materials in bulk because of their high surface area to volume ratio. lesson, made from checked teaching notes for this specification point.
Have a go first
Why can nanoparticles have different properties from the same material in bulk?
Listen
Nanoparticles have a very large surface area compared with their volume, so a high proportion of their atoms are at the surface. These surface atoms have fewer neighbours and different bonding environments from atoms inside a bulk solid, which can change melting point, reactivity, electrical conductivity, colour and catalytic activity. For example, gold is unreactive and yellow in bulk, but gold nanoparticles can appear red or purple and can act as catalysts. Titanium dioxide nanoparticles are effective in sunscreens because they absorb ultraviolet radiation while being transparent on the skin. A strong answer earns marks for these points. States that nanoparticles have a high surface area to volume ratio. Explains that a high proportion of atoms in a nanoparticle are at the surface. Links surface atoms with different bonding or coordination to altered physical and chemical properties. Gives a valid example, such as gold nanoparticles having a different colour or catalytic activity from bulk gold. A common slip: Claiming nanoparticles are a different chemical element from the bulk material. Instead, stating they are the same material with different particle size and surface effects. Exam tip: Always name the property that changes, such as colour, melting point or catalytic activity, and link it to the high surface area to volume ratio.
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