A
chemical compound is a pure
chemical substance consisting of two or more different
chemical elements that can be separated into simpler substances by
chemical reactions. Chemical compounds have a unique and defined
chemical structure; they consist of a fixed ratio of atoms that are held together in a defined spatial arrangement by
chemical bonds. Chemical compounds can be
molecular compounds held together by
covalent bonds,
salts held together by
ionic bonds,
intermetallic compounds held together by
metallic bonds, or
complexes held together by
coordinate covalent bonds. Pure
chemical elements are not considered chemical compounds, even if they consist of molecules that contain only multiple atoms of a single element (such as H
2, S
8, etc.), which are called
diatomic molecules or
polyatomic molecules.