States of Matter: Interactive Particle Simulation

What are the states of matter?

Everything around you is matter: anything that has mass and takes up space. Your desk, the water in your glass and the air you breathe are all matter. Matter is made of tiny particles (atoms and molecules) far too small to see, and how those particles are arranged and how they move decides the matter's state.

The three states you meet every day are:

• Solid: particles are packed tightly in a fixed pattern and only vibrate in place.
• Liquid: particles are close together but can slide past each other.
• Gas: particles are far apart and move fast in every direction.

NASA's Glenn Research Center sums it up: a solid holds its shape and its volume is fixed; a liquid takes the shape of its container but has a fixed volume; a gas fills its container, taking both the shape and the volume of the container.

The simulation above shows 40 particles of water. Drag the temperature slider and watch them go from a vibrating crystal (ice) to a sloshing puddle (liquid water) to a buzzing swarm (water vapor).

Solid, liquid and gas compared

Liquids and gases are both called fluids because they can flow. Gases are the only state you can easily squeeze into a smaller space, because their particles have so much room between them. That's how a bike pump packs air into a tire.

How do particles move in each state?

Particles are always moving, even in a solid. The hotter something is, the faster its particles move. That one idea explains every state:

• In a solid, strong attractions hold each particle in place. Heat makes them vibrate harder, like the particles in the simulation jiggling more as you warm the ice.
• In a liquid, particles have enough energy to break out of their fixed places, but they still attract each other, so they stay close and slide past one another. That's why a liquid flows and pools at the bottom of its container.
• In a gas, particles have so much energy that they break away from each other completely. They zoom in straight lines until they bump into each other or the walls, which is why a gas spreads out to fill any space.

The six phase changes

Changing from one state to another is called a phase change (or change of state). Three of them happen when matter gains heat, and three when it loses heat:

In the phase-change diagram, heating arrows are solid and cooling arrows are dashed. Each pair are opposites: melting and freezing, evaporation and condensation, sublimation and deposition.

Melting and freezing

When a solid warms up, its particles vibrate harder and harder. At the melting point, they shake loose from their pattern and the solid becomes a liquid. Ice melts at 0 °C (32 °F). Cool the liquid back down and it freezes at the same temperature, the freezing point.

Something surprising happens at the melting point: while ice is melting, its temperature stays at 0 °C until it has all melted. The heat is busy pulling particles out of their pattern instead of making them faster. The USGS gives the numbers for water: it takes 80 calories to melt one gram of ice, but only 100 more to heat that water all the way to boiling.

Water also has a famous quirk. Most substances shrink when they freeze, but water expands, so ice is less dense than liquid water and floats. If ice sank, lakes would freeze from the bottom up.

Evaporation, boiling and condensation

Evaporation happens when the fastest particles at the surface of a liquid escape into the air as a gas. It happens at any temperature, which is why a puddle dries on a cool day, just more slowly. Boiling is evaporation turned all the way up: at the boiling point, 100 °C (212 °F) for water at sea level, bubbles of vapor form all through the liquid. Water boils at a lower temperature on a high mountain, where the air pressure is lower.

Turning liquid water into vapor takes a lot of energy. The USGS gives 540 calories per gram, more than six times what it takes to melt ice. That's why sweating cools you down: as sweat evaporates, it carries heat away from your skin.

Condensation is the reverse. When a gas cools, its particles slow down and clump into drops of liquid. NOAA explains that condensation happens when there is more water vapor than the air can hold at its current temperature. It makes clouds, fog, dew and the drops on the outside of a glass of ice water, and it's a key step in the water cycle.

Sublimation and deposition

Some solids skip the liquid state entirely. Sublimation is a solid turning straight into a gas. The USGS describes it as the conversion between the solid and the gaseous phases of matter, with no intermediate liquid stage. Dry ice, frozen carbon dioxide, sublimates at −78.5 °C (−109.3 °F), which is why it makes a cold, smoky fog instead of a puddle. Choose Dry ice in the simulation and warm it past −78.5 °C to watch the particles fly straight out of the solid.

Snow and ice can sublimate too. The USGS notes it happens most with low humidity, dry winds, strong sunlight and low air pressure, such as high on Mount Everest, and that warm, dry chinook winds can make snow disappear in the American West.

Deposition is the reverse: a gas turning straight into a solid. The USGS gives snowflakes and frost as examples. On a cold, clear night, water vapor in the air can deposit as feathery frost on a car window without ever becoming liquid.

How many states of matter are there?

For everyday life, three: solid, liquid and gas. But scientists recognize more.

• Plasma is a fourth state. NASA's states of matter page explains that at very high temperatures, electrons are stripped from atoms, leaving charged particles. Lightning, neon signs and the Sun are plasma, and Britannica notes that nearly all the visible matter in the universe is in the plasma state.
• Bose-Einstein condensates form when certain atoms are cooled to within a whisker of absolute zero in the lab, and behave like one giant particle.

Pressure matters too, not just temperature. Earth's inner core is hotter than its outer core, yet National Geographic explains that the inner core stays solid because the pressure is so immense. See it in our layers of the Earth explorer.

Is a phase change a physical or chemical change?

A phase change is a physical change. The particles themselves don't change; only how they are arranged and how fast they move. Ice, liquid water and steam are all the same substance, H₂O, and you can turn one into another and back again. A chemical change, like burning wood or baking a cake, makes new substances that can't simply be turned back.

States of matter activities for kids

• Ice cube race. Put ice cubes on a plate, on a sunny windowsill and in a cup of warm water. Predict which melts first, then time them.
• Disappearing puddle. Draw a chalk outline around a puddle every hour on a sunny day to see evaporation.
• Cold glass. Fill a glass with ice water and watch drops of condensation appear on the outside. Where did that water come from? (The air.)
• Balloon gas. Stretch a balloon over the top of an empty bottle, then stand the bottle in a bowl of hot water. The air inside warms, its particles speed up and spread out, and the balloon inflates.
• Be the particles. Have kids stand shoulder to shoulder and sway (solid), walk slowly while staying close (liquid), then spread out and move quickly around the room (gas).

After the activities, try the Guess the state quiz in the simulation, then print the states of matter chart for a science notebook or the states of matter worksheet for review.

Explore the states of matter in 3D

Select Open in 3D to see 64 particles in a glass box over a heater, with a thermometer beside it. Drag the Temperature slider and watch the crystal shake apart into a liquid, then boil into a gas that fills the box. Switch to dry ice to see sublimation, or take the guided tour, which stops at each state and each phase change and runs the change for you. The 3D model uses the same particle rules as the 2D simulation. If your device can't show 3D graphics, the page shows the 2D simulation instead.

States of matter connect to almost every other science topic, from the water cycle to cooking and weather. If you want a full course that builds on them, compare the options in our best homeschool science curriculum guide or browse science programs, many of which families can pay for with a state scholarship or education savings account.