Solids have strong molecular bonds that don't allow for much movement, so they can maintain their shape and size. Liquids have weaker bonds that allow for some movement, so they can flow and take the shape of their container. Gases have even weaker bonds and their molecules move freely, spreading to fill any open space unless contained in a sealed container. The document also discusses the reversible changes of melting, freezing, evaporation and condensation using water as an example.

1. SOLIDS
LIQUIDS
GASES

2. SOLIDS GASESLIQUIDS
The molecules are
held together with
strong bonds.
They don’t move
very easily so
SOLIDS can keep
their own shape
and size
The molecules are
free to move around.
They can spread
around an open
space quickly and
freely. GASES can’t
keep their shape
unless they are kept
in a sealed container.
The molecules have
weaker bonds. They
can move around
slightly so LIQUIDS
can flow. They can’t
keep their shape
unless they’re in a
container.

3. ICE
STEAM
(WATER
VAPOUR)
WATER
HEAT HEAT
COOL COOL
condensefreeze
melt evaporate

4. What has caused the
droplets of water to
appear on the side of
the cold Coke can?

5. Burning is a non-reversible change

6. Burning is a non-reversible change