2.3 Chemical Properties and Reactions

States of Matter

The states of matter are the different forms substances can take—solid, liquid, or gas. Whether a substance is a solid, liquid, or gas depends on how close together its atoms or molecules are and how fast they move.

• Solids have a definite size and a definite shape. The atoms in a solid are very tightly packed and hardly move. Often they form regular patterns, like crystals. Wood, stone, and plastic are all examples of solids.
• Liquids have a definite volume but no definite shape. This means that if you have a cup of lemonade, it is a cup of liquid whether it’s in a gallon carton, in a glass, or in a puddle on the floor. Liquids can change shape because their atoms are farther apart than those of a solid. They can move more easily.
• Gases have no definite shape and no definite volume. The atoms in a gas are very far apart. They are always in motion. A gas will spread out if there’s a lot of space and compress if there is little space. For example, oxygen is spread out through the air, but it is compressed in an oxygen tank.