Bohr's Atomic Model

Bohr's Atomic Model

Bohr's Atomic Model was proposed by a Danish physicist Niels Bohr in 1913. It came in the existence with the modification in Rutherford's Atomic Model, in which he told that nucleus (postive charge) is surrounded by negatively charged electrons, Bohr's modified this atomic structure, by explaining that electrons moves in fixed orbit and not anywhere in between and he also explained that each orbit shell has fixed energy level. Rutherford basically explained nucleus of an atom and Bohr's modified that models into electrons and their energy levels.

Bohr's Atomic Model

A Danish physicist named Neil Bohr's in 1913 
proposed the Bohr atomic model. He modified the limitations and problems associated with the 
Rutherford atomic model.

Bohr's atomic model and the models after that explains the properties of atomic electrons on the basis of certain allowed possible values. The model explain how an atom absorb or emit radiation when electrons on subatomic level jump between the allowed and stationary states. German born Physicist James Frank and Gustav Hartz obtained the experimental evidence on these states.

According to Bohr's Atomic Model a small postively charged nucleus is surrounded by revolving negatively charged electrons in fixed orbits. He concluded that electrons will have more energy if it is located away from the nucleus whearas elctrelec have less energy if it is located near the nucleus.

Postulates of Bohr's Atomic Model

The Bohr's Atomic Model is based upon the following postulates :-

  • The electrons move around the nucleus in certain specifically permitted circular orbits known as energy levels.
  • An electron in a particular energy level is associated with a definite amount of energy.
  • While moving in a particular energy level or energy state, an electron neither loses nor gains energy . 
  • The energy of an electron in a particular energy state always remains fixed or stationary.
  • On observations of energy from an external source, an electron may jump from a lower energy level to a higher energy level. In coming back from a higher level to a lower energy level, the electrons emits energy.

Merits of Bohr's Atomic Model

The important merits of this model are as follows :

  • Explanation of the stability of Atom
  • Energy of Electron in a Particular Orbits
  • Radius of a particular orbit
  • Explanation of the Atomic Spectrum of Hydrogen

Defects in the Bohr's Atomic Model

Some important limitations of Bohr's Atomic Model are as follows :-

  • Bohr's model is unable to explain the spectra of atoms containing more than one electrons.
  • This model is unable to explain the fine spectrum of atoms . The fine spectrum of an atom contains many more closely spaced lines then predicted by Bohr's model.
  • The model is unable to explain the zeemans effect and Stark effect.
  • In Bohr's atomic model , electron is supposed to be a discrete particle moving in a well defined orbit.
  • Heisenberg uncertainty principle states that the Position and velocity can never be determined simultaneously and accurately. The principal gave a big set back to Bohr's model.
  • This model is unable to explain the mode of formation and geomatery of molecules which are formed by the union of two or more atoms.

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