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How tightly the molecules hold

Why Are Some Things Solid and Others Runny?

Solid, liquid and gas are the same molecules holding on with different strength.

1 Solid — lockedin place2 Liquid —touching butsliding3 Gas — flyingapart
Same molecules. Different grip.

  1. Step 1 of 5

    Molecules attract each other and also jiggle.

    State of matterAttractionpulls togetherHeat makesthem moveapart

    Attraction pulls them together; heat energy makes them move. Which of the two wins decides the state.

  2. Step 2 of 5

    In a solid, attraction wins.

    Solid Fixed positions — keepsits shapeLiquid Free to slide — takesthe container's shape

    Molecules vibrate but cannot leave their positions. That fixed arrangement is what makes a solid keep its shape.

  3. Step 3 of 5

    In a liquid, they slide but stay touching.

    Water in a glass Touching, but slidingfreely past each other

    Enough energy to break out of position, not enough to escape entirely. That is why liquids flow but do not expand to fill a room.

  4. Step 4 of 5

    In a gas, motion wins completely.

    Gas — spacingmolecules farapartLiquidtouchingSolidlocked together

    Molecules fly apart and spread to fill whatever contains them. They are so far apart that a gas is mostly empty space.

  5. Step 5 of 5

    Adding or removing heat switches states.

    Solid Add heat Liquid Add moreBothways

    Heat gives molecules the energy to break free; cooling lets attraction win again. Melting, boiling, condensing and freezing are all this one change.

    Glass is strange — it is rigid like a solid but its molecules are arranged as randomly as a liquid's.

The short version

Solid, liquid and gas are the same molecules with attraction or heat energy winning, and heating switches between them.

Try it yourself

Watch an ice cube in a warm pan until it melts and then boils. One substance, all three states, in minutes.

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