The Bohr Atom

In 1913 Niels Bohr came to work in the laboratory of Ernest Rutherford. Rutherford, who had a few years earlier, discovered the planetary model of the atom asked Bohr to work on it because there were some problems with the model: According to the physics of the time, Rutherford's planetary atom should have an extremely short lifetime. Bohr thought about the problem and knew of the emission spectrum of hydrogen. He quickly realized that the two problems were connected and after some thought came up with the Bohr model of the atom. Bohr's model of the atom revolutionized atomic physics.
The Bohr model consists of four principles:
1) Electrons assume only certain orbits around the nucleus. These orbits are stable and called "stationary" orbits.
2) Each orbit has an energy associated with it. For example the orbit closest to the nucleus has an energy E1, the next closest E2 and so on.
3) Light is emitted when an electron jumps from a higher orbit to a lower orbit and absorbed when it jumps from a lower to higher orbit.

The energy and frequency of light emitted or absorbed is given by the difference between the two orbit energies, e.g.,

E(light) = Ef - Ei

n = E(light)/h

h= Planck's constant = 6.627x10-34 Js

where "f" and "i" represent final and initial orbits.

With these conditions Bohr was able to explain the stability of atoms as well as the emission spectrum of hydrogen. According to Bohr's model only certain orbits were allowed which means only certain energies are possible. These energies naturally lead to the explanation of the hydrogen atom spectrum:
Bohr's model was so successful that he immediately received world-wide fame. Unfortunately, Bohr's model worked only for hydrogen. Thus the final atomic model was yet to be developed.

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C101 Class Notes
Prof. N. De Leon