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A chemical compound is a pure chemical substance consisting of two or more different chemical elements[1][2][3] that can be separated into simpler substances by chemical reactions.[4] Chemical compounds have a unique and defined chemical structure; they consist of a fixed ratio of atoms[3] 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 which contain only multiple atoms of a single element (such as H2, S8, etc.),[5] which are called diatomic molecules or polyatomic molecules.>>>>From>>>http://en.wikipedia.org/wiki/Chemical_compound