Unit 2 Review

Key Vocabulary

Pure Substance

A material with a fixed chemical composition and properties that cannot be physically separated.

Mixture

A physical combination of two or more substances that are not chemically bonded together.

Element

A pure substance made of only one type of atom that cannot be broken down.

Compound

A pure substance made of two or more elements chemically bonded in a fixed ratio.

Homogeneous Mixture

A mixture with a uniform composition where the different components are not visible.

Heterogeneous Mixture

A mixture with a non-uniform composition where you can easily see the different parts.

Elements

• An element is a pure substance that consists of only one type of atom.

• Elements cannot be broken down into simpler substances through any chemical reactions.

• Examples of elements include iron (Fe), oxygen (O), and aluminum (Al).

Compounds

• A compound is a pure substance made of two or more elements chemically bonded together.

• The properties of a compound are very different from its constituent elements.

• For example, water (H₂O) is a liquid formed from two gases, hydrogen and oxygen.

Homogeneous Mixtures

• These mixtures have a uniform composition, so you cannot see the different parts inside of them.

• They look like a single substance and are also known by the name of solutions.

• Some examples of these mixtures include air, saltwater, and metal alloys like brass.

Heterogeneous Mixtures

• These mixtures have a non-uniform composition, and you can easily see the different components.

• The different substances in the mixture remain distinct and are not mixed together evenly.

• Examples include a salad, a mixture of sand and water, or oil and water.