Molecule, n.: The ultimate, indivisible unit of matter. It is distinguished from the corpuscle, also the ultimate, indivisible unit of matter, by a closer resemblance to the atom, also the ultimate, indivisible unit of matter ... The ion differs from the molecule, the corpuscle and the atom in that it is an ion.
Even a vortex is a vortex in something. You can't have a whirlpool without water; and you can't have a vortex without gas, or molecules or atoms or ions or electrons or something, not nothing.