Final answer:
Elements and compounds are the two groups that pure substances can be broken down into. Elements are substances that cannot be broken down into chemically simpler components, while compounds are substances that can be broken down into chemically simpler components.
Step-by-step explanation:
Elements and compounds are both examples of pure substances. A substance that cannot be broken down into chemically simpler components is an element. For example, aluminum is an element. A substance that can be broken down into chemically simpler components (because it has more than one element) is a compound. For example, water is a compound composed of the elements hydrogen and oxygen.