Elements and Compounds


Key Concepts

· Elements are pure substances made up of only one type of atom.

· Elements cannot be broken down into simpler substances.

· Compounds are formed when two or more different elements chemically


· Compounds have properties different from the properties of the elements

that make them.

· Compounds are identified by chemical formulas.

· Some common compounds include water – H2O, salt – NaCl, and Carbon

Dioxide – CO2.

· A molecule is the smallest particle in a chemical element or compound that

has the chemical properties of that element or compound. Molecules are

made up of atoms that are held together by chemical bonds.

· Molecules can be made up of two like atoms (such as O2) or two different

types of atoms (such as H20).

· A chemical formula shows what elements a compound contains.

· Most substances found in nature are mixtures.

· Mixtures are substances that are mixed together but are NOT chemically


· Mixtures have no set ratio so they cannot be shown with a chemical

formula or symbol.

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