Bohr Model of the atom

Key Questions

  • Niels Bohr change the atomic theory by realizing that the electrons did not crash into the nucleus as would be expected in classical physics. Classical physics says that opposites attract and likes repel, so the negative electrons should be attracted to the positive nucleus. But not so. Why?

    Bohr took the ideas of Rutherford (nuclear model), Planck (quanta), Einstein (photoelectric effect and spectroscopy and created the Planetary Model.

    Bohr proposed that electrons were in energy levels (ground state) and absorbed photons of certain frequencies to move to a higher energy level (excited state). Then the electrons would release the photons in quantized amounts to return to ground state. The releasing of the photons is responsible for the line spectra given off by elements when excited.

    This idea was totally counter-intuitive and required a new physics.

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  • The main problem with Bohr's model is that it works very well for atoms with only one electron, like H or He+, but not at all for multi-electron atoms. Bohr was able to predict the difference in energy between each energy level, allowing us to predict the energies of each line in the emission spectrum of hydrogen, and understand why electron energies are quantized.

    Bohr's model breaks down when applied to multi-electron atoms. It does not account for sublevels (s,p,d,f), orbitals or elecrtron spin. Bohr's model allows classical behavior of an electron (orbiting the nucleus at discrete distances from the nucleus.

    The application of Schrodinger's equation to atoms is able to explain the nature of electrons in atoms more accurately.

  • The Bohr model was proposed by Niels Bohr in an attempt to explain why electrons don't crash into the nucleus. According to classical physics opposites attract and likes repel. However, electrons (-) don't move into the nucleus (+).

    Bohr suggested that this was because the electrons were in energy levels in the atomic space and moved from level to level by absorbing or releasing photons of certain frequencies.

    Bohr used Max Planck's ideas on quanta and the work of Bunsen and Kirchhoff in spectroscopy to support his model.

    The Bohr model revealed the problem with the current theories and need for a new physics.