States of Matter

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.

Solids

• 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).

Liquids

• A liquid has a definite volume, but takes the shape of its container.
• Examples of liquids include water and oil.

Gases

• 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

• 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.

Chemistry Encyclopedia