properties and states of matter

• In solids, the particles move by vibrating around fixed positions. This vibration gets faster when the solid is heated. As the particles vibrate more vigorously, they take up more space. That means, solids expand when heated.
• In liquids, the particles vibrate, but the particles are not in fixed positions. When the liquids are heated, the particles vibrate faster and move around faster. That means, the liquid expands when heated.
• In gases, the particles are far apart and move in straight lines until they collide with another particle or the walls of the container. When the gas is heated, the particles move faster and collide with more force and more frequently. The particles will take up more space in a heated gas, so gasses also expand when heated.
• Heating solids - When the solid is heated, heat energy is transferred to the particles in the solid. The more energy the particles have, the more they vibrate. As the particles vibrate more, they take up more space. The particles are still held in position by the attractive forces between them.
• Melting solids - When solids are heated more strongly, they melt and become liquid. The particles in a solid vibrate more and more, so much that the attractive forces between them are not strong enough to hold them in a fixed pattern. They can slide pass each other, not just vibrate. The forces are still strong enough for the particles to stay in touch with one another.
• Boiling liquids - When liquids are heated, they evaporate and boil. The particles are held weakly together. The particles move more as heat energy is transferred to them. Some particles have enough energy to break the weak attractive forces holding them together. These particles can move freely and escape as gas particles.
• Cooling gases - The particles in a gas are free to move anywhere and spread out, there are no forces holding them. When a gas gets cooler it condenses to form a liquid.

  When gas particles reach a cold surface, some of the heat energy from the particles transfers to the surface. The particles move less and get closer together to form a liquid.
• Freezing liquids - When a liquid freezes it becomes a solid. The particles in a liquid can move and flow past each other. As the heat energy is transferred from the particles to the surroundings, the particles move more slowly and the liquid gets cooler. The cooler the liquid, the less energy the particles have. They less energy the particles have, the less able they are to move or slide pass one another. Eventually, the particles have so little energy that they cannot flow anymore, they can only vibrate. They become arranged in a fixed pattern to form a solid.