Question

can a particle be a single atom?
can a particle be a molecule?

Answer 1

Its a relative question. There are subatomic particles (protons newborns) then it also can be described as part of a molecule, the H in H20.

Answer 2

wait what do you mean its a relative question?

Answer 3

its scaleable. depends on the size ratio. so, a particle of H20 is hydrogen. a particle of hydrogen is a proton, a particle of a proton is a quark

Answer 4

"particle" is a general term, it can be used for molecules, ions, atoms, subatomic particles, etc.