Question #50fef

1 Answer
Mar 12, 2016

None of the postulates hold true as explained below.


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Three main postulates by Bohr to improve the Rutherford's model of atom were:

  1. The electrons revolve around the nucleus of the atom in definite circular paths called orbits, or shells.
    This was similar to Rutherford's proposal that electron revolves around the central part of the atom much like planets rotate around the sun in our solar system.

  2. The electrons can only orbit the nucleus stably, in fixed orbits at a fixed distances from the nucleus. These orbits are associated with definite energies.

  3. While in these orbits, the electron's acceleration does not produce any electromagnetic radiation and energy loss. But any electron can gain or loose energy by jumping from one to another allowed energy levels by absorbing or radiating electromagnetic energy. The frequency #nu# of radiation was given by the expression: #E_1−
    where #h# is the Planck's constant.

First postulate stated that the electron orbits are planar. Whereas, modern quantum theory establishes that these are three dimensional. Hence does not hold.

Second postulate assumed that electron's position and energy can be predicted precisely. Heisenberg's Uncertainty principle did not support this postulate. As it predicted that both position and momentum of the any particle can not be ascertained with accuracy. #Deltaxcdot Delta p>=h/(2pi)# where #Deltax and Delta p# are uncertainly in position and momentum respectively.
In the modern theory we talk about probability of finding an electron.

Third postulated about orbits being defined by number #n=1, 2,3,4,...#. Modern quantum atomic theory defines shells, sub shells etc. Therefore we have following four to define the energy levels.

  1. Principal quantum number: #n#
  2. Angular momentum quantum number: #l#
  3. Magnetic quantum number: #m_l#
  4. Spin quantum number: #m_s#