A chemical is a substance made up of atoms and molecules that can undergo changes in composition and structure. Chemicals can be found in nature, such as in water and oxygen, or they can be synthesized in laboratories to create new materials, like plastics and medications. Chemicals are classified into different categories, including elements, compounds, and mixtures. Each type has unique properties and behaviors. Understanding chemicals is essential in fields like chemistry, biology, and environmental science, as they play a crucial role in various processes, from digestion to industrial manufacturing.