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Elements, Compounds and Mixtures

 How do Particles Move inside a Solid, Liquid and Gas?

Solid                  Liquid                   Gas
                   
Heating

Particle Motion in a Solid.

In a solid, the particles can vibrate
but they cannot move from one place to another.
If the solid is heated, the particles vibrate more and more
until the force of attraction between them is overcome.
The temperature at which this happens is called the melting point.
Above this temperature, the solid has become a liquid.

Particle Motion in a Liquid.

In a liquid the force of attraction between the particles
is weaker than it is in the solid.
It is still strong enough that the particles are held
close to each other but they are now free to move.
If the liquid is heated, the particles move faster and faster
until they overcome the force of attraction between them.
The temperature at which this happens is called the boiling point.
Above this temperature, the liquid has become a gas.
A liquid can also become a gas by evaporation.

What is Evaporation?

Some of the particles in a liquid are moving slow
and some are moving fast. Some of the particles
are moving fast enough to break through the surface
of the liquid and enter the air as a gas. This happens
at a temperature below the liquid's boiling point.
For example, water will evaporate at room temperature
(25 °C) but the boiling point of water is 100 °C.
The faster moving particles are hotter than the slower ones.
As the faster (hotter) particles leave the liquid by
evaporation, they take heat away from the liquid.
This is the reason that evaporation has a cooling effect. 

Particle Motion in a Gas.

A gas takes up a lot more space (occupies a greater volume)
than the boiling liquid it came from. This is called expansion.
In a gas, the particles move fast in random directions.
There is no force of attraction between the particles.

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