ChemistrySorting Things Into Solids, Liquids, and Gases
Atlas stands in a bright kitchen holding a wooden block in one hand and a glass of water in the other, while a balloon floats up beside him and colorful labels reading SOLID, LIQUID, and GAS hang on the wall behind him.
- Identify whether a familiar material is a solid, a liquid, or a gas.
- Explain that solids keep their shape, liquids pour and spread out, and gases fill their container.
- Compare a solid and a liquid using at least one observable property each.
- Sort everyday objects into the three groups: solids, liquids, and gases.
Key terms
- matter
- anything that takes up space, like a rock, water, or air
- solid
- matter that keeps its own shape, like a rock or a crayon
- liquid
- matter that pours and takes the shape of its container
- gas
- matter with no shape that spreads out to fill its space
Solids Keep Their Shape
A solid is matter that keeps its own shape no matter where you put it. A rock stays a rock and a crayon stays a crayon, even if you move them from a box to a table. You can hold a solid in your hand and it will not change shape on its own. Because solids hold their shape, they are usually the easiest kind of matter to pick up and stack.
Liquids Pour and Spread
A liquid is matter that pours and spreads out to take the shape of whatever holds it. Water, juice, and milk are all liquids, and if you pour juice into a cup, it becomes the shape of that cup. Liquids flow from place to place, which is why you can spill them. Unlike solids, liquids do not keep one fixed shape; they change shape to match their container every time.
Gases Fill Their Container
A gas is matter that has no shape of its own and spreads out to fill all the space it is in. The air inside a balloon is a gas, and it spreads to fill the whole balloon from corner to corner. Gases keep spreading until something stops them, like the walls of a container. To tell a gas apart, ask whether it fills its whole space completely instead of keeping a fixed shape.
Worked examples
Decide what kind of matter orange juice is.
- Pour the juice into a cup and watch what it does.
- It flows and takes the shape of the cup, which solids cannot do.
- Matter that pours and takes its container's shape is a liquid.
Answer: Orange juice is a liquid because it pours and takes the shape of the cup.
Is the air inside a balloon a solid, liquid, or gas?
- Notice the air spreads out to fill the whole balloon.
- It has no shape of its own and fills every corner.
- Matter that fills its whole container is a gas.
Answer: The air inside the balloon is a gas because it fills the whole balloon.
Activity
Drag each item into the correct bucket — Solid, Liquid, or Gas.
Practice
Name one solid, one liquid, and one gas from your home.
Compare a rock and a glass of water using one property.
Common mistakes to avoid
- Ice is a liquid because it is wet and cold.Ice keeps its own shape until it melts, so it is a solid, even though it feels cold.
- A gas is not matter because you cannot see it.A gas is matter because it takes up space and fills its container, like air in a balloon.
Check your understanding
You pour orange juice and it takes the shape of the glass. What kind of matter is orange juice?
Your friend says ice is a liquid because it is wet and cold. Is your friend right?
Which of these is a gas?
Recap
Matter comes in three forms: solids keep their shape, liquids pour and take the shape of their container, and gases spread out to fill their whole space. Asking what a material does helps you sort it into the right group.
Reflect
Which form of matter do you notice most often around you?