2.1 Properties of Matter

• Properties used to describe matter can be classified as extensive or intensive.
• Every sample of a given substance has identical intensive properties because every sample has the same composition.
• Three states of matter are solid, liquid, and gas.
• Physical changes can be classified as reversible or irreversible.

2.2 Mixtures

• Mixtures can be classified as heterogeneous mixtures or as homogeneous mixtures, based on the distribution of their components.
• Differences in physical properties can be used to separate mixtures.

2.3 Elements and Compounds

• Compounds can be broken down into simpler substances by chemical means, but elements cannot.
• If the composition of a material is fixed, the material is a substance. If the composition may vary, the material is a mixture.
• Chemists use chemical symbols to represent elements, and chemical formulas to represent compounds.

2.4 Chemical Reactions

• During a chemical change, the composition of matter always changes.
• Four possible clues to chemical change include a transfer of energy, a change in color, the production of a gas, or the formation of a precipitate.
• During any chemical reaction, the mass of the products is always equal to the mass of the reactants.