What Are the States of Matter?

Everything Is Made of Particles

Look around you. Your desk, the air you're breathing, the water in your glass — they're all made of incredibly tiny particles (atoms and molecules) that are always moving. The difference between a solid, a liquid, and a gas isn't what the particles are made of — it's how fast they're moving and how close together they are.

Temperature is the key. When you add heat energy to matter, particles move faster. When you remove heat, they slow down. This relationship between temperature and particle movement is what creates the three main states of matter.

Solids: Particles Locked in Place

In a solid, particles are packed tightly together in a fixed pattern. They vibrate in place but don't move around. This is why solids have a definite shape and a definite volume — a rock stays rock-shaped whether you put it on a table or in a box. The strong attractions between particles keep everything locked in position.

Think of particles in a solid like students sitting in assigned seats. They can wiggle and shift, but they stay in their spots.

Liquids: Particles That Slide

Add enough heat to a solid and the particles start moving fast enough to break free from their fixed positions. Now they can slide past each other while still staying relatively close together. This is a liquid. Liquids have a definite volume but no definite shape — they take the shape of whatever container holds them. Pour water into a round glass, and it becomes round. Pour it into a square container, and it becomes square.

Particles in a liquid are like students at a school dance: moving around the room, bumping into each other, but staying inside the gymnasium.

Gases: Particles Set Free

Add even more heat and particles move so fast they completely break free from each other. In a gas, particles spread out to fill whatever space is available. Gases have no definite shape and no definite volume. Open a bottle of perfume, and the gas molecules spread across the entire room. That's because gas particles move in every direction at high speed, bouncing off walls and each other.

Phase Changes: Transforming Between States

When matter changes from one state to another, it's called a phase change. These changes happen at specific temperatures for each substance:

• Melting — solid → liquid (ice melts at 0°C / 32°F)
• Freezing — liquid → solid (water freezes at 0°C / 32°F)
• Evaporation/Boiling — liquid → gas (water boils at 100°C / 212°F)
• Condensation — gas → liquid (steam on a cold mirror)
• Sublimation — solid → gas directly (dry ice turning to fog)

During a phase change, the temperature stays constant even though you're adding heat. All the energy goes into breaking the bonds between particles rather than making them move faster. That's why ice water stays at exactly 0°C until all the ice has melted — the heat is busy breaking bonds, not raising temperature.

Where Kids Get Stuck

The biggest misconception is that molecules stop moving in a solid. In fact, molecules in a solid are constantly vibrating — they just can't move freely from place to place. They're locked in fixed positions, vibrating like a crowd standing in line, all fidgeting but not changing positions. In liquids, molecules slide past each other. In gases, molecules fly freely and fill whatever container they're in.

Another confusion is about melting and dissolving. Children often say sugar "melts" in water, but it actually dissolves — the sugar molecules separate and mix with water molecules. Melting is a state change caused by heat. Dissolving is a mixing process. Sugar melts at about 186°C; it dissolves in water at room temperature. These are fundamentally different processes.

Students also struggle with what happens during phase changes. When ice melts at 0°C, the temperature stays at 0°C until all the ice is liquid — the added energy goes into breaking bonds between molecules rather than raising the temperature. This concept, called latent heat, is why a glass of ice water stays cold until the last piece of ice melts.

Phase Changes and Energy

Every state change involves energy being added or removed. The six phase changes have specific names: melting (solid to liquid), freezing (liquid to solid), evaporation (liquid to gas), condensation (gas to liquid), sublimation (solid to gas), and deposition (gas to solid). Sublimation is the most surprising — dry ice (solid CO₂) skips the liquid phase entirely and turns directly into gas. Frost forming on a window is deposition — water vapor turning directly into ice crystals.

There's also a fourth state of matter that most elementary curricula skip: plasma. Though rarely discussed, plasma makes up over 99% of the visible universe. Stars, lightning, neon signs, and the aurora borealis are all plasma, which forms when gas is heated so intensely that electrons separate from atoms.

Try This at Home

• Ice observation journal — Place an ice cube on a plate and record observations every 5 minutes. Note when it's fully melted. Leave it in the sun — when does the water disappear?
• Oobleck — Mix cornstarch and water to explore a non-Newtonian fluid that acts like a solid under pressure and a liquid when relaxed.
• Condensation catch — Pour ice water into a glass on a humid day. Water droplets form on the outside — that's water vapor from the air condensing.
• Balloon expansion — Put a balloon on a bottle, place in hot water (balloon inflates) then ice water (deflates). This shows how gas expands and contracts with temperature.

For more experiments, see: Free Science Tools for the Classroom.

🧊 Explore the States of Matter Tool

Last reviewed: May 2026