Hydrogen line spectrum

The discussion of emission spectroscopy will be concluded by a description of a rather unusual application. Bay and Steiner have measured atomic hydrogen concentrations in the presence of molecular hydrogen by microwave excitation of the atomic hydrogen line spectrum. With low power fed into the gas (ca. 5 watts), there is not enough energy available for the dissociation of molecular hydrogen and subsequent excitation. Thus the measured intensities of the atomic hydrogen lines correspond to the concentrations of atoms already present in the reaction mixture. The method is curiously similar to that adopted to detect atoms and free radicals by mass spectrometry (see Section 3). 

Line spectra for multi-electron atoms are more complex than the hydrogen line spectrum, and thus are less easily explained in an explicit fashion at a middle school, high school, or even first year undergraduate level. However, discussions of this topic with respect to the hydrogen atom allow for the instructor to point out many important features of rudimentary quantum mechanics. Among these are the quantized nature of the electrons in atoms, the Bohr model of one-electron atoms, the dual wave-particle nature of light, the... 

Figure 7.7 (a) a continuous spectrum containing all wavelengths of visible light (indicated by the initial letters of the colors of the rainbow), (b) The hydrogen line spectrum contains only a few discrete wavelengths. 

Fig. 15-2. Contrast between the continuous spectrum of a hot tungsten ribbon and the line spectrum of a hydrogen discharge tube.

To explain why hydrogen atoms emit the line spectrum, we must seek a model with the... 

Historically, the visible emission lines shown in Figure 15-3 were the first atomic hydrogen lines discovered. They were found in the spectrum of the sun by W. H. Wollaston in 1802. In 1862, A. J. Angstrom announced that there must be hydrogen in the solar atmosphere. These lines were detected first because of the lesser experimental difficulties in the visible spectral region. They are called the "Balmer series because J. J. Balmer was able to formulate a simple mathematical relation among the frequencies (in It S). The ultraviolet series shown in Figure 15-3 was... 

Eventually, other series of lines were found in other regions of the electromagnetic spectrum. The Lyman series was observed in the ultraviolet region, whereas the Paschen, Brackett, and Pfund series were observed in the infrared region of the spectrum. All of these lines were observed as they were emitted from excited atoms, so together they constitute the emission spectrum or line spectrum of hydrogen atoms. 

This accounts for the fact that the line spectrum of hydrogen shows only lines having certain wavelengths. In order for the electron to move in a stable orbit, the electrostatic attraction between it and the proton must be balanced by the centrifugal force that results from its circular motion. As shown in Figure 1.7, the forces are actually in opposite directions, so we equate only the magnitudes of the... 

Figure 2.1 Electronic orbitals and the resulting emission spectrum in the hydrogen atom, (a) Bohr orbitals of the hydrogen atom and the resulting spectral series, (b) emission spectrum of atomic hydrogen. The spectrum in (b) is calibrated in terms of wavenumber (P), which is reciprocal wavelength. The Balmer series, which consists of those transitions terminating on the second orbital, give rise to emission lines in the visible region of the spectrum. ( 1990 John Wiley Sons, Inc. Reprinted from Brady, 1990, by permission of the publisher.)...

Although it proved possible to conclude from the results of further experiments with the perester that succinimidyl radicals from this source could abstract benzylic hydrogen from toluene, the reaction system presented further difficulties which are still unresolved. For example, when solutions of NBS and MBN are mixed in the dark, a high concentration of [32] is immediately produced. Whilst this helped to establish the origin of the 27-line spectrum, it constitutes a fresh mechanistic puzzle. 

How do you think the lines you observed in the hydrogen emission spectrum relate to the energy of the electrons in a hydrogen atom Include a diagram in your answer. 

Scientists of the nineteenth century lacked the concepts necessary to explain line spectra. Even in the first decade of the twentieth century, a suitable explanation proved elusive. This changed in 1913 when Niels Bohr, a Danish physicist and student of Rutherford, proposed a new model for the hydrogen atom. This model retained some of the features of Rutherford s model. More importantly, it was able to explain the line spectrum for hydrogen because it incorporated several new ideas about energy. As you can see in Figure 3.8, Bohr s atomic model pictures electrons in orbit around a central nucleus. Unlike Rutherford s model, however, in which electrons may move anywhere within the volume of space around the nucleus, Bohr s model imposes certain restrictions. 

Look again at the line spectrum for hydrogen shown in Figure 3.7. 

The agreement between this relation and the observed line spectrum of hydrogen was far too good to be a mere coincidence. While the details of the election orbits employed by Bohr in his calculation may not be a part of the cnrrent paradigm, the concept of electronic energy levels is here to stay. 

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