Matter has mass and occupies space. In a solid, close particles vibrate about fixed positions, so the substance usually keeps its shape and volume. In a liquid, close particles move past one another: the liquid flows but keeps an almost fixed volume. Gas particles are far apart and move throughout the available space.
A gas compresses easily because spaces between its particles can decrease. The particles themselves do not normally shrink. Attraction helps hold solids and liquids together. Particle diagrams represent arrangement using enlarged dots; the dots are not actual particle colours or sizes. A still diagram cannot directly show continuous motion.
Example 1
Why can air in a sealed syringe be compressed more easily than water?
Air particles have large spaces between them that can decrease. Water particles are already close together, so its volume changes very little under the same moderate pressure.
Example 2
A substance keeps its volume but takes the shape of a beaker. Which particle model fits?
A liquid model: close particles can move past one another, giving a nearly fixed volume but a changing shape.
Watch out:They vibrate about fixed positions. A solid retaining its shape does not mean its particles are motionless.
A model of matter practice | Year 7 Science | Ascent Arcade