Structure of Atom

05 Bohr’s Model of The Atom

  • Neil Bohr proposed the Bohr model of atom in 1915 with the modification of Rutherford’s model of atom.
  • Rutherford’s model had introduced nuclear model of atom, in which he explained that a nucleus (positively charged) is surrounded by negatively charged electrons.
  • Bohr modified this atomic structure model. He explained that electrons move in fixed orbital’s (shells) and not anywhere in between and he also explained that each orbit (shell) has a fixed energy level.
  • Rutherford basically explained nucleus of an atom which Bohr modified by explaining that model into electrons and their energy levels.

Postulates of Bohr’s Model of an Atom:

  • The atom-consists of a small (positively charges) nucleus at its centre.
  • The whole mass of the atom is concentrated at the nucleus and the volume of nucleus is smaller than the volume of the atom by a ratio of about 1:105.
  • All the protons and neutrons of the atom are contained in the nucleus.
  • The electrons of the atom revolve round the nucleus in definite circular paths known as orbits or shells which are designed as K, L, M, N  etc. numbered as (n)=1, 2, 3, 4 etc. outward from the nucleus.
  • Each orbit is associated with a fixed amount of energy. Therefore, these orbits are also known as energy levels or energy shells.
  • The energy of the atom changes when an electron jumps from state (energy level) to another state (energy level).
  • As long as an electron remains in a particular orbit, it does not lose or gain energy.

Limitations of Bohr’s Model of an Atom

  • Bohr’s Atomic model violates the Heisenberg Uncertainty Principle.
  • It could not explain the spectra obtained from larger atoms.
  • Bohr’s model of an atom failed to explain Zeeman Effect (effect of magnetic field on the spectra of atoms).
  • It also failed to explain the Stark effect (effect of electric field on the spectra of atoms).

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