Chemical elements are pure substances that consist of only one type of atom, distinguished by their atomic number, which is the number of protons in their nucleus. Each element has unique properties and can combine with other elements to form compounds. The periodic table organizes these elements based on their atomic structure and chemical properties, making it easier to understand their relationships. There are currently 118 known chemical elements, ranging from hydrogen, the lightest, to oganesson, the heaviest. Elements can be classified into metals, nonmetals, and metalloids, each exhibiting different characteristics. Understanding chemical elements is fundamental to the study of chemistry and the natural world.