The model of the atom has constantly been changing throughout history due to new discoveries of the property of an atom.  Starting in BC and continuing until around the 1930s the atomic model has been changed several times with the finding of the electron, neutron, and proton.  The model is also changed when a scientist discovers a theory that disproves the temporary model and so the others must change it.  Although not many major discoveries regarding the atomic model have been found since 1930, there is still a high certainty that changes are yet to come.