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 about a nucleus of protons and neutrons.
A Chemical Compound is a substance consisting of two or more chemical elements that are chemically combined in fixed proportions.
A Molecule is the smallest particle of an element or compound that retains the chemical 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.
