Atomic Structure :  Bohr Model

 In 1913, Niels Bohr proposed a model for the hydrogen atom which explained the spectrum of a hydrogen atom based upon the following assumptions:

 Bohr Model for the Hydrogen Atom The electron in a hydrogen atom travels around the nucleus is a circular orbit. The energy of the electron is directly proportional to its distance from the nucleus. There are a limited number of specific allowed energy levels, i.e., the orbitals are quantized. The angular momentum of the electron in any orbital is an integral multiple of Planck's constant divided by 2. When light is absorbed, the electron jumps from a lower energy level to a higher energy level.  When light is emitted, the electron falls from a higher energy level to a lower energy level. The energy of light absorbed or emitted is equal to the difference in the energy levels of the orbits between which the electron jumps of falls. To simplify these assumptions, remember these key words and concepts: CIRCULAR ORBIT in which the electron travels around the nucleus. Energy Distance energy of an orbital is directly proportional to the distance from the nucleus. QUANTIZED limited number of countable allowed energy levels. ANGULAR MOMENTUM fixed for each energy level. Absorption is Low E to High E Emission is High E to Low E Energy of absorption/emission = E difference of energy levels.

Problems with the Bohr Model

1. The model is only valid for the hydrogen atom (with one electron).
2. The first assumption concerning the electrons in fixed circular orbits violates the laws of classical mechanical physics.
3. The ANGULAR MOMENTUM assumption violates the Heisenberg uncertainty principle.
 Heisenberg Uncertainty Principle - It is impossible to determine the position (x) and the momentum (mv) of a particle simultaneously with certainty. In the Bohr model, it is assumed that there are fixed angular momentums for each quantized orbital. Werner Heisenberg

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