What was Heisenberg's contribution to the atomic model?
Heisenberg introduced the uncertainty principle according to which the electron's position and momentum can never be determined accurately. This was in contradiction to Bohr's theory. The uncertainty principle contributed to the development of quantum mechanics and hence the quantum mechanical model of the atom.
Heisenberg's uncertainty principle was a big blow to the Bohr's model on the atom.
The Bohr's atom assumed that the electrons revolved around the nucleus in specified circular paths. In this assumption, we assume that we have the knowledge of the electron's trajectory.
What Heisenberg said was the complete opposite. His principle dictates that it is impossible for us to accurately determine the electron's trajectory.
Further developments resulted in the concept of discarding the idea of finding the electron's path and relying on the probability of finding the electron in a region in space.