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States of Matter

Grades 4-7 · Concept Explainer

Key Points

  • ✓Matter exists in different states: solid, liquid, gas, and plasma.
  • ✓Solids have a definite shape and volume.
  • ✓Liquids have a definite volume but take the shape of their container.
  • ✓Gases have no definite shape or volume.
  • ✓Matter can change states by adding or removing heat.

Everything around you is made of matter! Matter can exist in different forms called states. The most common states are solid, liquid, and gas. A solid has a definite shape and volume, like an ice cube. A liquid has a definite volume but takes the shape of its container, like water. A gas has no definite shape or volume and spreads out to fill its container, like the air we breathe. Sometimes, matter can also exist as plasma, which is like a superheated gas with charged particles.

Worked Example

If you have an ice cube (solid water) at -5°C and heat it up, what happens?

  1. Step 1: The ice cube warms up. Its temperature increases until it reaches 0°C.
  2. Step 2: At 0°C, the ice cube starts to melt and changes into liquid water. The temperature stays at 0°C until all the ice has melted.
  3. Step 3: The liquid water warms up. Its temperature increases until it reaches 100°C.
  4. Step 4: At 100°C, the liquid water starts to boil and changes into steam (water vapor). The temperature stays at 100°C until all the water has turned into steam.

Answer: The ice cube melts into liquid water, and then the liquid water boils into steam.

Try It Yourself

1. What state of matter is a rock?

2. What happens to water when it freezes?

3. Explain how the arrangement of molecules differs between a solid, a liquid, and a gas.

Watch Out For These Mistakes

  • Thinking that all liquids are water.
  • Believing that gases are always invisible.
  • Forgetting that matter can change states.