Rocket pours a handful of dry beans onto a plate and packs them into a tight square. "Pretend these are particles," he says.
"Of what?" Raven asks. "Ice," he says, and he jiggles the plate gently. The beans wiggle but stay in their places.
He jiggles harder. The beans slide over each other and spread into a loose puddle. "Now they are water."
Raven tips the plate, and the bean puddle flows to one side. "What do you notice? They stay touching, but they slide."
Nova dims her light and hovers higher. "What would a gas look like on your plate?" she asks. "Think about how much room each bean would need."
Rocket flicks three beans so they skitter across the whole table. "Like that," he says. "Far apart, bouncing everywhere."
Raven writes: particles, spacing, motion.
The particle model explains the states of matter. Its big idea is that matter is made of tiny particles that are always in motion.
The particles may be atoms or molecules. Gases and liquids are made of molecules or inert atoms that are moving about relative to each other.
In a solid, the atoms are closely spaced and may vibrate in position, but they do not change relative locations.
In a liquid, the molecules are constantly in contact with others, but they slide past one another.
In a gas, the particles are widely spaced except when they happen to collide.
| State | Spacing of particles | Motion of particles | What you see |
|---|---|---|---|
| Solid | Closely spaced, in fixed positions | Vibrate in place | Keeps its shape and volume |
| Liquid | Close together, always in contact | Slide past each other | Flows, keeps its volume, takes the container's shape |
| Gas | Far apart, mostly empty space | Move fast in random directions until they collide | Fills the whole container, easy to squash |
Gas particles are far apart compared to their size. Most of the volume of a gas is the empty space between its particles.
That is why gases are easy to compress. A large amount of oxygen can be stored in a small tank, and it expands when released.
Gas particles move in straight lines until they collide with another particle or with the wall of their container.
The faster the particles move, the more kinetic energy they have. The temperature of a gas is proportional to the average kinetic energy of its particles.
Solids and liquids are called condensed states. Their particles are far closer together than the particles of a gas.
The particles of most solids are packed tightly in an orderly arrangement. Their motion is limited to vibration about a fixed point.
Solids are almost completely incompressible. Squeeze an ice cube and it does not get smaller.
In a liquid, the particles are free to move over each other, but they are still attracted to each other. That is why a liquid holds together in a cup.
| Statement | True or false? |
|---|---|
| Gas particles are far apart compared to their size. | ? |
| Liquid particles are not attracted to each other at all. | ? |
| Solids are almost completely incompressible. | ? |
| The particles in a solid never move. | ? |
| Gas particles travel in straight lines until they collide. | ? |
Sharp thinking. Tomorrow is Bench Lab: you will test shape, volume and squashing with water, ice and a bag of air.