Limitations of Bohr's model of the atom

• Bohr's biggest contribution in his model was to introduce quantum principles to classical physics, but his model had a few limitations:
• Spectra of Large atoms:
  • The Bohr model could only successfully explain the hydrogen spectrum.
  • It could NOT accurately calculate the spectral lines of larger atoms.
  • The model only worked for hydrogen-like atoms
    • That is, if the atom had only one electron.
• Relative Spectra Intensity
  • Bohr's model could not explain why the intensity of the spectra lines were NOT all equal.
    • This suggests that some transitions are favoured more than others.
• Hyperfine spectral lines
  • With better equipment and careful observation, it was found that there were previously undiscovered spectral lines
  • These were named Hyperfine lines and they accompanied the other more visible lines.
  • Bohr's model could not explain why this was the case due to the lack of equipment and development in quantum physics.
    • The reason for these lines is actually because of a hyperfine structure of atoms.
    • Solved through developments into Matrix Mechanics
• The Zeeman effect
  • It was found that, when hydrogen gas was excited in a magnetic field, the produced emission spectrum was split.
  • Bohr's model could not account for this
    • Solved by accounting for the existence of a tiny magnetic moment of each electron.
• Stationary states
  • Although Bohr stated that electrons were in stationary states, he could not explain why.
    • The reason is covered later
• Mixture of Sciences
  • The Bohr model was a mixture of quantum and classical physics
  • This is an issue because it was thought that quantum physics was completely irrelevant and different to classical physics.

HINT: A useful mnemonic for remembering these is: Some Retards Have Zebra Stripes.