A molecule is an aggregate of at least two atoms in a definite placement that are held together by chemical forces (also called chemical bonds). A molecule can contain atoms of the same element or atoms of two or more elements, always in a fixed ratio. Thus, a molecule is not always a compound, which, by definition, is made up of two or more elements.
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Full Professor of Organic Chemistry at the University of Granada, with a long-standing research career in Computational Chemistry and molecular modeling and design.