<P> A chemical substance, also known as a pure substance, is a form of matter that consists of molecules of the same composition and structure . It cannot be separated into components by physical separation methods, i.e., without breaking chemical bonds . Chemical substances can be simple substances, molecules, chemical compounds, or alloys . </P> <P> Chemical substances are often called' pure' to set them apart from mixtures . A common example of a chemical substance is pure water; it has the same properties and the same ratio of hydrogen to oxygen whether it is isolated from a river or made in a laboratory . Other chemical substances commonly encountered in pure form are diamond (carbon), gold, table salt (sodium chloride) and refined sugar (sucrose). However, in practice, no substance is entirely pure, and chemical purity is specified according to the intended use of the chemical . </P>

A substance made of two or more elements in a certain ratio