An "element" is a pure substance that cannot be broken down into simpler substances by chemical means. Each element is made up of atoms, which are the basic building blocks of matter. Elements are organized in the Periodic Table, where each one is represented by a unique symbol, such as H for hydrogen or O for oxygen. Elements can be classified into metals, nonmetals, and metalloids based on their properties. They combine in various ways to form compounds, which are substances made of two or more different elements. For example, water is a compound made of two hydrogen atoms and one oxygen atom.