Matter commonly exists as solid, liquid or gas, differing in particle spacing, motion and order.
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Matter exists in three common states because the balance between intermolecular attraction and thermal kinetic energy differs. In a solid, particles are held in fixed positions and only vibrate, so the shape and volume are fixed. In a liquid, particles stay close together but slide past one another, so the volume is fixed while the shape changes to fit the container. In a gas, particles are far apart and move freely, so a gas fills whatever space it is given. Raising the temperature or lowering the pressure weakens the attractions relative to motion, which drives phase transitions.
Key ideas: Compare the strength of intermolecular forces with thermal energy, roughly kT, to predict the state. Melting and boiling points rank forces: ionic and metallic solids melt high, molecular solids low. Density order is usually solid > liquid >> gas, with gas densities near 1 g/L versus about 1000 g/L for liquids. Phase changes at constant pressure happen at fixed temperature while heat is absorbed or released.
Common mistakes and connections: Students often say particles in a solid do not move; they vibrate. Another error is thinking the particles themselves expand when heated, when really the spacing grows. Water is an exception to the solid being denser than the liquid. Links to phase diagrams, intermolecular forces and kinetic theory.
Particles in a solid vibrate in fixed positions; raise the temperature slider to see them loosen into a liquid and then fly apart as a gas. The interactive lesson shows this as a live animation or chart.
Water exists as ice below 0°C, as liquid between 0°C and 100°C, and as steam above 100°C at 1 atm.
Matter commonly exists as solid, liquid or gas, differing in particle spacing, motion and order.
States of Matter is a beginner topic in States of Matter & Solutions. It needs no earlier chemistry lessons and is a good starting point.
It is one of the first topics in States of Matter & Solutions, so no earlier lesson in this area is required.
The next topics in States of Matter & Solutions are Kinetic Molecular Theory and Plasma.
Yes. The interactive lesson includes a self-check question on States of Matter, and the States of Matter & Solutions quiz draws on every topic in this area.
States of Matter is topic 1 of 109 in States of Matter & Solutions.