Matter is anything that has mass and takes up space. In a solid, particles are packed closely and mainly vibrate in place, giving solids a definite shape and volume. In a liquid, particles stay close but can slide around, so liquids have a definite volume but take the shape of their container. In a gas, particles move far apart and spread out, so gases change shape and volume to fill available space. The differences come from particle motion and the forces holding particles together.
Comprehension Check
Which state of matter has a definite shape and a definite volume?
Why does a liquid take the shape of its container?
Changing State
Heating or cooling changes how fast particles move. When a solid gains energy, it can melt into a liquid; when a liquid gains more energy, it can boil into a gas. Cooling does the reverse: gases condense into liquids, and liquids freeze into solids. Sometimes a solid skips the liquid stage and becomes a gas directly; this is called sublimation, like dry ice. The temperature at which a substance changes state depends on the substance itself, so not all materials melt or boil at the same temperature.
Comprehension Check
What happens to particle motion when a substance is heated?
Which change of state skips the liquid phase?
Beyond the Basics: Plasma
Besides solids, liquids, and gases, there is plasma—a state where gas particles have so much energy that some electrons break away. This mix of charged particles conducts electricity and responds to magnetic fields. Lightning and the Sun are natural examples of plasma, and plasma screens and neon signs use it in technology. Learning about plasma shows how adding energy can create new behaviors that are not seen in ordinary gases.
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