Matter occurs in four states: solids, liquids, gases, and plasma. Often the state of matter of a substance may be changed by adding or removing heat energy from it. For example, the addition of heat can melt ice into liquid water and turn water into steam.
- A solid has a definite shape and volume.
- Examples of solids include ice (solid water), a bar of steel, and dry ice (solid carbon dioxide).
- A liquid has a definite volume, but takes the shape of its container.
- Examples of liquids include water and oil.
- A gas has neither a definite volume nor a definite shape.
- Examples of gases are air, oxygen, and helium.
- Plasma has neither a definite volume nor a definite shape.
- Plasma often is seen in ionized gases. Plasma is distinct from a gas because it possesses unique properties. Free electrical charges (not bound to atoms or ions) cause plasma to be electrically conductive. Plasma may be formed by heating and ionizing a gas.
- Stars are made of plasma. Lightning is plasma. You can find plasma inside fluorescent lights and neon signs.