Matter in any state is composed of small particles – molecules, atoms, or ions. Differentiate the terms above in Italics.
Molecules: A molecule is the smallest particle of a substance that can normally exist separately and retain the characteristics of the substance, e.g. O2, H2, Cl2 are molecules.
Atoms: An atom is the smallest particle of an element that can take part in a reaction and is considered the basic unit of matter, e.g. O, H, Cl are atoms.
Ions: An ion is any atom or a group of atoms that has a resultant charge due to loss or gain of electrons, e.g. O2-, H1+, Cl1-– are ions.