Sizes of Particles & their Properties (AQA GCSE Chemistry)

How big are nanoparticles?

• Particles can be placed into one of three categories according to their diameter:

  • Coarse particles (also called particulate-matter or dust)

  • Fine particles

  • Nanoparticles

• Since the diameter in metres of these tiny particles would be a very small number, it is easier to use a smaller scale such as micrometers or nanometres

• A micrometre is 1x10^-6 of a metre and a nanometer is 1x10^-9 of a metre

• Sometimes the terms PM2.5 and PM10 are used to describe fine and coarse particles respectively

  • PM stands for Particulate Matter and the 2.5 or 10 refers to the particle size in micrometres

  • These are used to describe the type of air pollution that is not gaseous

The size of particles

The diameter in nanometres used to classify particles

• Nanoparticles are between 1 and 100 nanometres in size and usually contain only a few hundred atoms

• Atoms and simple molecules are around 100 times smaller than this

• Nanoparticles are much smaller than fine particles which have diameters of between 100 and 2500 nm

• This field of study is called nanoscience and research into the production and application of nanoscience is called nanotechnology

The relative size of particles

Diagram showing the size of nanoparticles relative to other objects and substances

Surface to volume ratio

• One of the most interesting features of nanoparticles is their very high surface area to volume ratio

• As particles decrease in size, their surface area increases in relation to their volume

• As the side of a cube decreases by a factor of 10, the surface area to volume ratio increases by a factor of 10

• This is why nanoparticles may have properties different from those for the same materials in bulk

• It may also mean that smaller quantities are needed to be effective than for materials with larger particle sizes

• Fullerenes (nanoparticles made of carbon) behave very differently to larger compounds of carbon like diamond and graphite

• The surface area to volume ratio is an important feature in catalysis and surface chemistry

  • The higher the ratio then the more surface area is available for reaction, hence the better the catalyst

Surface area to volume ratio in cubes

This diagram shows the surface area to volume ratio of three different sizes cubes