Bohr’s theory of hydrogen

By 1925 it was realized that the classical ideas that described matter didn t work at the atomic level. Some progress—Planck s quantum theory, Einstein s application of quantum theory to light, Bohr s theory of hydrogen, de Broglie s relationship—had been made, but it was all very specific and not generally applied to atoms and molecules. 

The concept of chemical periodicity is central to the study of inorganic chemistry. No other generalization rivals the periodic table of the elements in its ability to systematize and rationalize known chemical facts or to predict new ones and suggest fruitful areas for further study. Chemical periodicity and the periodic table now find their natural interpretation in the detailed electronic structure of the atom indeed, they played a major role at the turn of the century in elucidating the mysterious phenomena of radioactivity and the quantum effects which led ultimately to Bohr s theory of the hydrogen atom. Because of this central position it is perhaps not surprising that innumerable articles and books have been written on the subject since the seminal papers by Mendeleev in 1869, and some 700 forms of the periodic table (classified into 146 different types or subtypes) have been proposed. A brief historical survey of these developments is summarized in the Panel opposite. 

Spectroscopy was to prove indispensable in unlocking the structure of atoms, particulary their electronic stmcture— but those developments would depend on other, later researchers. Max Planck s analysis of blackbody radiation and Bohr s theory of the hydrogen spectrum are just two examples. 

Millikan s experiment did not prove, of course, that (he charge on the cathode ray. beta ray, photoelectric, or Zeeman particle was e. But if we call all such particles electrons, and assume that they have e/m = 1.76 x Hi" coulombs/kg. and e = 1.60 x 10" coulomb (and hence m =9.1 x 10 " kg), we find that they fit very well into Bohr s theory of the hydrogen atom and successive, more comprehensive atomic theories, into Richardson s equations for thermionic emission, into Fermi s theory of beta decay, and so on. In other words, a whole web of modem theory and experiment defines the electron. The best current value of e = (1.60206 0.00003) x 10 g coulomb. 

By 1903. llie wave theory of light based oil Maxwell s equations was well established, but certain phenomena would not fit in. It seemed that emission and absorption of hght occur discontinuously. This led Einstein to (lie view that the energy is concentrated in discrete particles. It was a revolutionary idea, very hard to understand, as the successes of the wave theory were undeniable. It seemed that light had to be understood sometimes as waves, sometimes as particles, and physicists had to get used to it, The idea was incorporated into Bohr s theory of the hydrogen atom and forms an essential part of it. 

This was the state of our knowledge of the structure of the atom when Langmuir, the modern scientific conquistador, attempted to invade the tiny world of the atom. There was an unmistakable conflict between Bohr s theory of the hydrogen atom and the conception of Lewis. Chemists could see but little use in the Bohr atom. They wanted an atom which would explain chemical reactions. The first World War over, Langmuir undertook to reconcile the two theories by publishing his concentric shell theory of atomic structure. 

Briefly describe Bohr s theory of the hydrogen atom and how it explains the appearance of an emission spectrum. How does Bohr s theory differ from concepts of classical physics ... 

Between 1912 and 1925, Bohr s theory of the atom gave rise to a conceptual framework for the study of matter on many fronts. Applying the theory to predict the energy levels and therefore the emission frequencies of atoms more complicated than hydrogen—say, helium with two electrons, lithium with three, and so on— led to the concept of electronic shells about the nucleus, the outer shell less tightly bound, and it is these outer-shell electrons that determine the element s spectrum. It should be pointed out that the theory was not fully successful in predicting the spectral lines of the elements that are more complicated than hydrogen. 

Explain how the existence of fine spectra is consistent with Bohr s theory of quantized energies for the electron in the hydrogen atom. 

Some important successes of classical quantum theory Bohr s theory of the atomic spectrum of hydrogen... 

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