Chemistry
The particle model
Why can you smell perfume across the whole room? A simple model explains a surprising amount.
What you need first
Someone opens a perfume bottle at the other end of the room, and moments later you can smell it from your seat. A tea bag colours hot water all by itself. And a puddle disappears in the sun without anyone wiping it away. Behind all of this is a single idea, one of the most important in all of chemistry.
Everything is made of particles
The particle model says: all substances are made of tiny particles, far too small for any classroom microscope. These particles are constantly moving, jiggling, bumping, and flying around without ever standing still. Between them is empty space. And crucially: the warmer a substance is, the faster its particles move. Heat is nothing other than particle motion.
Water (liquid). Particles move faster.
A model, not a photograph
The particle model is a model: a deliberately simplified picture of reality, not a photograph. We imagine the particles as little spheres, even though real particles are more complicated. That is perfectly fine, because a good model does not have to be perfect. It has to explain observations and allow predictions. And that is exactly what the particle model does remarkably well.
Dissolving, evaporating, boiling, diffusion
With the model, everyday puzzles suddenly make sense. Dissolving: water particles swarm around the sugar and carry its particles away until they are spread invisibly fine. Evaporating: especially fast water particles (H₂O) manage to escape from the puddle into the air, which is why warm water evaporates faster. Boiling: heat water to 100 °C and so many particles are fast enough that vapour bubbles form in the middle of the liquid. That holds at normal , the pressure you usually get at . High in the mountains the air pressure is lower, so water boils there below 100 °C. Diffusion: scent and colour particles wander by random collisions towards wherever few of them are. That is why perfume spreads through a room, and why tea spreads faster in hot water than in cold.
Exercises
0 of 6 solvedTime to try it yourself. You can't break anything, every attempt counts.
What does the particle model say about all substances?
What happens to a substance's particles when you heat it?
At how many degrees Celsius does water (H₂O) boil at normal air pressure at sea level?
In the particle model, heat is nothing other than ….
You heat tea water from 20 °C to 80 °C. By how many degrees Celsius does the temperature rise?
Match each everyday process to the matching explanation from the particle model.
Where this leads