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In most materials, atoms are joined
in tiny groups called molecules. The
shapes of molecules and the way
they pack together can help explain
how different materials behave.
Molecules
Steaming ahead
Molecules are always jiggling about. When
they get hot, they move further and faster.
When water heats up, the molecules may
start moving so fast that they escape into
the air as water vapour.
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Science and technology
Snow may look
like white powder,
but if you look
closely you can
see thousands of
tiny crystals as
clear as glass.
Frozen solid
Cold molecules move slowly,
allowing them to pack together
more easily. When water
freezes, the molecules line up in
neat rows, forming ice crystals.
Clouds appear when water
vapour cools down and
becomes liquid again.
The grey mist is made of
millions of tiny liquid droplets.
Melt:
As a solid heats up,
its molecules move faster until
they break free from each other
and move separately, turning
the solid into a liquid.
Solidify:
As a liquid cools, its
molecules lose energy and move
more slowly. Eventually they start
sticking together, turning the
liquid into a solid.
If a liquid is poured into a
jar or bottle, it takes the
shape of its container and
stays in place.
Solid
Liquid
