Again your most welcome on our blog. Today I wanna discuss Shortcomings of Bohr’s Theory. In my last post I’ve discussed Excitation & Ionisation of Atoms & Molecules.
Shortcomings of Bohr’s Theory:
i). An individual line of Hydrogen spectrum when examined under a high resolving spectroscope. It is found that a single line is accompanied by a number of faint lines. The structure is known as fine structure.
The fine structure cannot be explained by Bohr’s theory. Afterwards fine structure was explained by taking electron spin into accounts.
ii). The theory is only applicable to single electron atom such as Hydrogen, He+,Li++. It does not explain the spectra of complex atoms.
iii). The success of Bohr’s theory in explaining the effect of magnetic field on spectral line is only partial.
iv). The theory explain Normal Zeeman effect but failed to explain anomalous Zeeman effect.
We will discuss Zeeman effect more clearly a in our upcoming posts.
v). Bohr’s theory cannot explain the variation in intensity of spectral lines of an element. The variation in intensity is explained by Quantum mechanics.
According to Wikipedia :
The Bohr model gives an incorrect value for the ground state orbital angular momentum: The angular momentum in the true ground state is known to be zero from experiment.
Although mental pictures fail somewhat at these levels of scale, an electron in the lowest modern “orbital” with no orbital momentum, may be thought of as not to rotate “around” the nucleus at all, but merely to go tightly around it in an ellipse with zero area (this may be pictured as “back and forth”, without striking or interacting with the nucleus).
This is only reproduced in a more sophisticated semiclassical treatment like Sommerfeld’s.
Still, even the most sophisticated semiclassical model fails to explain the fact that the lowest energy state is spherically symmetric – it doesn’t point in any particular direction….Read more