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States of Matter

Solids, Liquids, Gases & Plasma


Plasma typically is seen as an ionized gas.

Plasma typically is seen as an ionized gas.

Luc Viatour

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.
Some introductory chemistry texts name solids, liquids, and gases as the three states of matter, but higher level texts recognize plasma as a fourth state of matter.


  • 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.

Learn More

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