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(a) Using Balmer's generalized formula, show that a hydrogen series identified by the integer \(m\) of the lowest level occupies a frequency interval range given by $$ \Delta v=c R_{\mathrm{H}} /(m+1)^{2} $$ (b) What is the ratio of the range of the Lyman series to that of the Pfund series?

Short Answer

Expert verified
The ratio of the range of the Lyman series to that of the Pfund series is 9.

Step by step solution

01

Derive the frequency interval for a hydrogen series

To derive the frequency interval range formula, consider the Balmer's generalized formula v = \( R_{H}(( \frac{1}{m^2} - \frac{1}{n^2} ))\). The difference between the maximum and minimum frequencies, which is the frequency interval (∆v), is given when \(n\) varies between \(m+1\) and infinity. So, we have ∆v = \( R_{H}( \frac{1}{m^2} − \frac{1}{(m+1)^2})\) = \(c R_{H} / (m+1)^{2} \). So we obtained the required frequency interval range formula.
02

Calculate the ratio for the Lyman and Pfund series

The Lyman series corresponds to \(m=1\), and the Pfund series corresponds to \(m=5\). Using the derived equation: ∆v = \(c R_{H} / (m+1)^{2}\), we can write the ratio of the range of the Lyman series to that of the Pfund series as: \( \frac{∆v_{Lyman}}{∆v_{Pfund}} = \frac{cR_H / (1+1)^2}{cR_H / (5+1)^2} = \frac{1/4}{1/36} = 9\). Hence, the ratio is 9

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Key Concepts

These are the key concepts you need to understand to accurately answer the question.

Balmer Formula
The Balmer formula is foundational to understanding hydrogen's spectral emissions. It specifically relates to the wavelengths of the visible spectral lines of hydrogen. As a practical application under the broader context of the Rydberg formula, the Balmer series calculates the wavelengths with a principal quantum number, n, greater than 2 and converging on the second energy level of the hydrogen atom (n=2).

In mathematical terms, it is given by \[\begin{equation}\lambda = \frac{364.56 nm}{(m^2 - 2^2)}\end{equation}\]where \(m\) is an integer greater than or equal to 3. The Balmer formula is a specific case of the Rydberg formula and has been quintessential in the field of spectroscopy for identifying hydrogen gas and studying the detailed quantum behavior of electrons within an atom.
Frequency Interval in Spectroscopy
In spectroscopy, the concept of a frequency interval is central to distinguishing between different energy transitions. The frequency interval, denoted by \(\Delta v\), indicates the range of frequencies over which a particular spectral series occurs. This range is defined by the difference between the highest and lowest frequencies emitted when an electron transitions between energy levels.

For hydrogen's spectral series, derived from the Rydberg formula, the frequency interval can be expressed as a function of the principal quantum number of the lowest energy level involved in the transitions (\[\begin{equation}\Delta v = c R_H / (m+1)^2\end{equation}\]). This reveals the intervals' dependence on the Rydberg constant and the speed of light, showing how they determine the fine structure of spectral lines.
Lyman Series
The Lyman series of hydrogen spectral lines arises when an electron transitions from higher energy levels (n > 1) down to the first energy level (n=1). These transitions produce ultraviolet radiation, which stems from the energy released during the electron's 'jump' to the ground state. The mathematical representation of the series, part of the larger Rydberg equation, is fundamental for calculating the wavelengths and frequencies of the emitted radiation.

The importance of the Lyman series extends to several scientific fields, including astronomy, where it helps in the observation and understanding of faraway stars and galaxies. Its spectral lines are often used as a diagnostic tool to detect hydrogen in cosmic phenomena.
Pfund Series
In contrast to the Lyman series, the Pfund series originates from electron transitions to the fifth energy level of the hydrogen atom (\[\begin{equation}n=5\end{equation}\]). These transitions emit photons mostly in the infrared region of the electromagnetic spectrum, making them less visible to the naked eye but invaluable for infrared spectroscopy. The Pfund series is less well known than the Balmer or Lyman series due to the less energetic transitions of its lines and their application in more specialized areas of science and technology, such as the study of astrophysical objects in the infrared spectrum.
Rydberg Constant
The Rydberg constant is a fundamental physical constant that plays a pivotal role in atomic physics. Its value is essential for calculating the wavelengths of photons emitted or absorbed during electron transitions between energy levels in a hydrogen atom. Symbolized as \(R_H\), its current accepted value is approximately \(1.097 \times 10^{7} m^{-1} \).

This constant is derived from empirical observations and is a cornerstone of the Rydberg formula, which describes the spectral lines of not only hydrogen but also other hydrogenic (single-electron) atoms. Its most recognizable application is in its contribution to the Balmer formula, and its significance in assisting the quantification of atomic spectra cannot be overstated.

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Most popular questions from this chapter

Consider a body rotating freely about a fixed axis. Apply the Wilson- Sommerfeld quantization rules, and show that the possible values of the total energy are predicted to be $$ E=\hbar^{2} n^{2} / 2 I \quad n=0,1,2,3, \ldots $$ where \(I\) is its rotational inertia, or moment of inertia, about the axis of rotation.

Calculate the shortest wavelength of the Lyman series lines in hydrogen. Of the Paschen series. Of the Pfund series. In what region of the electromagnetic spectrum does each lie?

Assuming that an amount of hydrogen of mass number three (tritium) sufficient for spectroscopic examination can be put into a tube containing ordinary hydrogen, determine the separation from the normal hydrogen line of the first line of the Balmer series that should be observed. Express the result as a difference in wavelength.

(a) Show that when the recoil kinetic energy of the atom, \(p^{2} / 2 M\), is taken into account the frequency of a photon emitted in a transition between two atomic levels of energy difference \(\Delta E\) is reduced by a factor which is approximately \(\left(1-\Delta E / 2 M c^{2}\right)\). (Hint: The recoil momentum is \(p=h v / c .\) ) (b) Compare the wavelength of the light emitted from a hydrogen atom in the \(3 \rightarrow 1\) transition when the recoil is taken into account to the wavelength without accounting for recoil.

A beam of \(\alpha\)-particles, of kinetic energy \(5.30 \mathrm{MeV}\) and intensity \(10^{4}\) particle/sec, is incident normally on a gold foil of density \(19.3 \mathrm{~g} / \mathrm{cm}^{3}\), atomic weight 197 , and thickness \(1.0 \times 10^{-5} \mathrm{~cm}\). An \(\alpha\) particle counter of area \(1.0 \mathrm{~cm}^{2}\) is placed at a distance \(10 \mathrm{~cm}\) from the foil. If \(\Theta\) is the angle between the incident beam and a line from the center of the foil to the center of the counter, use the Rutherford scattering differential cross section, (4-9), to find the number of counts per hour for \(\Theta=10^{\circ}\) and for \(\Theta=45^{\circ} .\) The atomic number of gold is 79 .

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