States of Matter: Solids, Liquids and Gases Explained
The states of matter are the different forms that matter can take, and the three that students learn first are solid, liquid and gas. This guide gives clear definitions, everyday examples, a look at how matter changes from one state to another, an anchor chart layout and activities for the classroom.
States of matter
Matter is anything that has mass and takes up space. A desk is matter. So is the water in a glass and the air inside a balloon. Even things that are hard to see, like air, count as matter because they take up space.
Matter shows up in different forms, and those forms are the states of matter. The state depends on how the tiny particles inside the material are arranged and how they move. Students do not need to see particles to understand the idea. They only need to know that everything is built from particles too small to see.
What are the three states of matter
When a student asks what are the three states of matter, the answer is solid, liquid and gas. Each one behaves in a way that is easy to test with simple objects. A states of matter definition for each one fits on a card:
- Solid: has its own shape and its own volume. It does not change shape when you move it to a new container.
- Liquid: has its own volume but no shape of its own. It takes the shape of the container that holds it.
- Gas: has no shape and no fixed volume. It spreads out to fill whatever container it is in.
Volume means the amount of space something takes up. That word is worth saying aloud a few times, because it is the key to telling a liquid from a gas.
Solids
The particles in a solid are packed close together and stay in place. They still move a little, by jiggling, but they do not slide past each other. That is why a solid holds its shape.
Here are solids that are easy to find in a classroom:
- a pencil
- a book
- an ice cube
- a rock
- a metal spoon
- a wooden ruler
Some solids are made of many small pieces, such as sand, salt and flour. Pour them and they flow a bit like a liquid, so students often get confused. Each grain is a tiny solid with its own shape. Take one grain out and it does not spread out to fit a container.
Liquids
The particles in a liquid are close together but they can slide past one another. That is why a liquid pours and why it takes the shape of its container.
- water
- milk
- juice
- cooking oil
- liquid soap
- honey
Liquids come in thick and thin forms. Honey pours slowly and water pours quickly, yet both are liquids. A good test is to pour the same amount of water into a tall glass, a wide bowl and a narrow jar. The shape changes each time. The amount stays the same.
Gases
The particles in a gas are far apart and move around freely. A gas is not stuck in one place. It spreads out until it fills all the space it can.
- the air around us
- helium in a balloon
- the carbon dioxide in the bubbles of a fizzy drink
- water vapor
- the gas in a stove or heater
Students may say that steam is a gas. The invisible part is water vapor, which is the gas. The white cloud above a kettle is made of tiny drops of liquid water that formed as the vapor cooled. This is a good moment to slow down and look closely, because it shows that what we see does not always match what we say.
Three states of matter examples side by side
Students can compare the three states of matter quickly with a chart. Here is a layout that works on the board or on paper:
- Shape: a solid keeps its shape, a liquid takes the shape of its container, and a gas fills its container.
- Volume: a solid and a liquid have a fixed volume, while a gas does not.
- Particles: packed close and held in place for a solid, close but sliding for a liquid, and far apart and moving freely for a gas.
- Examples: a pencil, a glass of milk and the air inside a balloon.
This kind of states of matter chart helps with sorting and comparing. Ask students to add rows of their own, such as whether the material can be poured or squeezed.
Changes of states of matter
Matter can change from one state to another when it is heated or cooled. These changes of states of matter have names that students can learn one at a time:
- Melting: a solid becomes a liquid when it is heated. An ice cube melts into water.
- Freezing: a liquid becomes a solid when it is cooled. Water turns into ice.
- Evaporation: a liquid becomes a gas. A puddle dries up as the water goes into the air.
- Condensation: a gas becomes a liquid. Water drops form on the outside of a cold glass.
Two other changes skip the liquid step. In sublimation, a solid turns straight into a gas, as dry ice does. In deposition, a gas turns straight into a solid, as frost forms on a cold window. These two are good extras for older students.
Boiling is a fast kind of evaporation. It happens all through the liquid once it reaches its boiling point. Evaporation without boiling happens only at the surface, at lower temperatures.
States of matter in water
Water is the best material for teaching this topic, because students see all three states in daily life. It is ice when frozen, liquid when poured, and water vapor when it evaporates. At normal air pressure, water freezes at 0 degrees Celsius (32 degrees Fahrenheit) and boils at 100 degrees Celsius (212 degrees Fahrenheit).
Water has an interesting quirk. Most materials are more tightly packed as solids than as liquids. Water is the other way around, because ice takes up more space than the same amount of liquid water. That is why ice floats and why a sealed bottle of water can crack in a freezer.
The same three states carry through the whole water cycle. If your class is studying how water moves from the ground to the sky and back again, the water cycle post follows evaporation and condensation step by step.
Heat and the states of matter
Heat is what moves matter from one state to another. Adding heat makes particles move faster. Taking heat away slows them down. This is the cause behind every change listed above.
It also shows up outside the classroom. Some power plants heat water until it becomes steam, and the steam turns a turbine to make electricity. The renewable energy sources post covers where that heat can come from.
The four states of matter and plasma
Many lists include a fourth state. If someone asks about the four states of matter, the fourth is plasma. Plasma forms when a gas becomes so hot that its atoms lose some of their electrons. Lightning, neon signs and the Sun all involve plasma.
Elementary lessons usually stick to three states, and that is a sound place to start. Plasma can be a short extension for curious students. Scientists describe more unusual states too, but those belong to later grades.
States of matter anchor chart
A states of matter anchor chart gives students something to check as they work. One layout uses three columns, one for each state:
- the name of the state at the top
- a short note on shape and volume
- a simple picture of the particles, drawn as dots (close and still, close and sliding, or far apart)
- a list of examples the class has found
Below the columns, add a row of arrows labeled with the change names: melting, freezing, evaporation and condensation. Students can place a sticky note with an example on each arrow.
Activities and games for states of matter
Sort the objects
Fill a tray with classroom objects and a few cards with written names, such as milk, a spoon or air. Students sort everything into three groups. Ask them to explain their choice for tricky items, such as sand or a sponge.
Pour test
Pour the same amount of water into three different containers and compare the shape each time. Then place a pencil in each container. Students see that the liquid changes shape and the solid does not.
Melt and freeze
Put an ice cube in a clear cup and let it melt in the classroom. Students record what they see in a drawing of the cup and the water. For the next step, freeze the water again. An adult handles any heating, as with a kettle or a hot plate.
Games for states of matter
Games for states of matter work well as a warm-up or as a station. Here are two that need only paper:
- Which state? Read out a material, such as steam, a bar of soap or lemonade. Students hold up one finger for solid, two for liquid or three for gas.
- Change cards. Write a change on one card, such as an ice cube turning into water, and its name on another. Students match the pairs face down, like a memory game.
Practice material
Reading passages give students a chance to see these ideas in real texts. The snow and ice reading passages look at winter weather and freezing states of matter, with 10 texts, tasks and answer keys across 72 pages for grades 1 to 5. The science reading comprehension packet has ten STEM topics across 48 pages for grades 2 to 5, and the topics include matter, with complete answer keys.
For water in its different forms, the water cycle reading passages are 63 pages for grades 3 to 5 and cover evaporation, condensation, precipitation and collection with full questions and answer keys. The rain reading passages have 10 passages on precipitation, the water cycle and storm science for grades 2 to 6, with a lesson plan and answer keys. The iceberg formation passages explore glacier calving, water buoyancy, tabular bergs and polar ecology across 62 pages for grades 2 to 6.
Frequently asked questions
Is sand a solid or a liquid?
Sand is a solid. It pours because it is made of many tiny grains, but each grain keeps its own shape and volume.
Is steam a gas?
Water vapor is the gas. The white cloud we see above hot water is made of tiny drops of liquid that formed when the vapor cooled.
Does air count as matter?
Yes. Air has mass and takes up space. A balloon filled with air shows that it takes up room, since the balloon swells as air goes in.
What grade learns the states of matter?
Students meet the idea in the early grades and return to it later with more detail. The reading packs below cover grades 1 to 6, so you can choose one that fits your class.
