What is the achievement of neil bohr?

Answer 1

After Ernest Rutherford showed that atoms consisted of an exceedingly small, positive nucleus; while the electrons were far outside of this center; it was unclear how such an arrangement could result in the emission spectra of such atoms. Scientists tried to show that only certain vibrations could result within this atomic setup -- in much the same way that only certain vibrations are permitted on a violin string -- but without success. The problem they kept running into was their assumption that electrons could be any distance from this nucleus.

Neils Bohr adopted the radical postulate that electrons were permitted ONLY in very discrete radial orbits around the nucleus. Thus, an electron could be orbitting at a distance of 1.00 angstroms from the nucleus, or at 2.00 angstroms, but never at .99 A, 1.01 A, or 1.50 A. While this Bohr Model was eventually deemed too simplistic, it was an incredibly radical shift in the understanding of atomic structure.