States of Matter
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flagWhat you'll discover
- arrow_forwardDescribe solids, liquids and gases using the particle model
- arrow_forwardLink temperature to the kinetic energy of particles
- arrow_forwardExplain why temperature pauses at the melting and boiling points
- arrow_forwardCompare melting and boiling points across different substances
The particle model
All matter is made of tiny particles in constant motion, and the three common states differ only in how those particles are arranged and how much they move. In a solid, particles sit in a fixed, regular lattice and merely vibrate in place — that is why solids hold their shape. In a liquid, particles still touch but can slide past one another, letting the liquid flow and take its container's shape. In a gas, particles break free entirely and fly in straight lines until they collide, filling every corner of whatever space they are given.
Watch the simulation switch between all three as you drag the temperature slider.
Temperature is particle motion
Temperature measures the average kinetic energy of the particles. Heat a substance and its particles vibrate, jostle or fly faster; cool it and they slow down. At −273 °C, absolute zero, particle motion reaches its minimum — nothing can be colder.
This explains everyday observations: gases expand when heated because faster particles hit the walls harder and more often; smells spread faster in a warm room because the gas particles carrying them travel faster; and sugar dissolves quicker in hot tea because energetic water particles break the crystal apart sooner.
Plateaus: the hidden energy of melting
Heat ice steadily and its temperature climbs — until 0 °C, where it sticks. The thermometer pauses while the ice melts, then resumes climbing through the liquid range, and pauses again at 100 °C while the water boils. These flat sections of the heating curve are the plateaus you can see in the simulation's graph.
During a plateau the added energy, called latent heat, is spent breaking the bonds between particles instead of speeding them up. That is why steam at 100 °C scalds far worse than water at 100 °C: it carries the entire latent heat of vaporisation, ready to release into your skin.
Every substance has its own thresholds
Melting and boiling points are fingerprints of a substance, set by how strongly its particles attract one another. Water melts at 0 °C and boils at 100 °C. Oxygen's molecules attract so weakly that it is a gas until −183 °C and only freezes at −218 °C. Iron's atoms grip each other so strongly that it stays solid until 1538 °C and boils at a furious 2862 °C.
Switch substances in the simulation and notice that the behaviour is identical — only the temperatures shift. The particle model is universal; the bond strength is what changes.