The Challenge: Make Ice
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How do the molecules behave in the three states?
In a solid there are strong bonds linking the molecules into a lattice structure. The molecules
can vibrate but cannot move around, so the solid has a fixed shape. However
in a liquid some of these bonds have been broken, allowing the molecules
to move freely and take up the shape of the container. In water vapor
even more of these bonds have been broken so that not only does the gas
take up the shape of the container but it is able to expand and fill the
entire volume of the container, no matter how big it is.
A crucial point is that in liquids molecules are moving at different speeds all
the time. How fast a molecule moves depends on how much energy it has.
This is called kinetic energy. It's a liquid's average energy that we
measure when we find the temperature. More energy and so faster-moving
molecules means the liquid will be hotter, less energy means the liquid
will be colder.