A chemical element is a substance that cannot be divided or changed into different substances by ordinary chemical methods. The smallest particle of such an element is an atom, which consists of electrons centered around a nucleus of protons and neutrons.
A molecule is the smallest particle of an element or compound that retains the characteristics of the element or compound.
An ion is an atom or group of atoms with a net electric charge, having lost (cation) or gained (anion) an electron.
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