A chemical element is a pure substance that cannot be broken down into simpler substances by chemical means. Each element is defined by the number of protons in its atomic nucleus, known as the atomic number. For example, the element hydrogen has one proton, while carbon has six. Elements are the building blocks of matter and combine in various ways to form compounds. There are currently 118 known chemical elements, organized in the Periodic Table. Each element has unique properties, such as melting point, density, and reactivity. Elements can be classified as metals, nonmetals, or metalloids, depending on their characteristics and behavior in chemical reactions.