Review: states of matter and particles
All matter is made of tiny particles that are always moving. We draw them as dots because a model is not a photograph. In a solid the particles are close together in a pattern and only vibrate in place, so a solid keeps its shape. In a liquid they are close but slide past one another, so a liquid flows and takes the shape of its container. In a gas they are far apart and move freely, so a gas fills its container. A gas has mass, and so does the air in a pumped-up ball. Heating adds thermal energy, and the particles move faster. Cooling takes thermal energy away, and the particles slow down. Melting, freezing, evaporating, boiling and condensing are changes of state. They are physical changes, because the substance is still the same. Sand pours like a liquid, but every grain is a small solid.
| Change | Name | Heat… |
|---|---|---|
| solid to liquid | melting | goes in |
| liquid to gas | evaporating or boiling | goes in |
| gas to liquid | condensing | goes out |
| liquid to solid | freezing | goes out |
| Container | Mass at the start (g) | Mass after a day (g) |
|---|---|---|
| closed jar | 230 | 230 |
| open dish in the sun | 230 | 215 |
State-of-matter poster. Draw three boxes of dots for a solid, a liquid and a gas, and write two properties under each. Add four arrows between the boxes for melting, freezing, evaporating and condensing, and write on each arrow whether heat goes in or out.