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Is energy emitted or absorbed when the following electronic transitions occur in hydrogen: (a) from \(n=4\) to \(n=2,(\mathrm{~b})\) from an orbit of radius \(2.12 \AA\) to one of radius \(8.46 \AA\), (c) an electron adds to the \(\mathrm{H}^{+}\) ion and ends up in the \(n=3\) shell?

Short Answer

Expert verified
In summary, for the given electronic transitions in hydrogen: (a) energy is emitted as the electron moves from n=4 to n=2, (b) energy is absorbed when the orbit radius changes from 2.12 Ã… to 8.46 Ã…, and (c) energy is emitted when an electron adds to the H+ ion and ends up in the n=3 shell.

Step by step solution

01

Case (a): Transition from n=4 to n=2

Let's calculate the energy change during the transition: \(\Delta E = E_f - E_i = -\cfrac{13.6\,\mathrm{eV}}{n_f^2} - \left(-\cfrac{13.6\,\mathrm{eV}}{n_i^2} \right)\) \(\Delta E = -\cfrac{13.6\,\mathrm{eV}}{2^2} + \cfrac{13.6\,\mathrm{eV}}{4^2}\) \(\Delta E = -3.4\,\mathrm{eV} + 0.85\,\mathrm{eV} = -2.55\,\mathrm{eV}\) The negative result indicates that energy is emitted in this transition.
02

Case (b): Orbit radius changes from 2.12 Ã… to 8.46 Ã…

To determine the principal quantum numbers corresponding to the initial and final orbits, we can use the formula for the radius: \(r_n = a_0n^2 = 0.529n^2 \AA\) Solve for n: \(n_i^2 = \cfrac{2.12\,\mathrm{\AA}}{0.529\,\mathrm{\AA}}\) \(n_i^2 = 4\) So, initial quantum number \(n_i = 2\). For final quantum number: \(n_f^2 = \cfrac{8.46\,\mathrm{\AA}}{0.529\,\mathrm{\AA}}\) \(n_f^2 = 16\) So, final quantum number \(n_f = 4\). Now, let's calculate the energy change during the transition: \(\Delta E = E_f - E_i = -\cfrac{13.6\,\mathrm{eV}}{n_f^2} - \left(-\cfrac{13.6\,\mathrm{eV}}{n_i^2} \right)\) \(\Delta E = -\cfrac{13.6\,\mathrm{eV}}{4^2} + \cfrac{13.6\,\mathrm{eV}}{2^2}\) \(\Delta E = -0.85\,\mathrm{eV} + 3.4\,\mathrm{eV} = 2.55\,\mathrm{eV}\) The positive result indicates that energy is absorbed in this transition.
03

Case (c): Electron adds to H+ ion and ends up in n=3 shell

For an electron adding to H+ ion, the initial energy level would be infinity since the electron is very far from the nucleus. Using the energy level formula: \(E_i = -\cfrac{13.6\,\mathrm{eV}}{n_i^2} = -\cfrac{13.6\,\mathrm{eV}}{\infty} = 0\,\mathrm{eV}\) Now calculate the final energy level when the electron is in the n=3 shell. \(E_f = -\cfrac{13.6\,\mathrm{eV}}{n_f^2} = -\cfrac{13.6\,\mathrm{eV}}{3^2}\) \(E_f = -1.51\,\mathrm{eV}\) Now let's calculate the energy change during the transition: \(\Delta E = E_f - E_i = -1.51\,\mathrm{eV} - 0\,\mathrm{eV} = -1.51\,\mathrm{eV}\) The negative result indicates that energy is emitted in this transition.

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Key Concepts

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

Energy Emission and Absorption
When electrons make transitions between different energy levels in a hydrogen atom, energy either gets absorbed or emitted. This process depends on whether the electron is moving to a higher or lower energy state.

Elecrons absorb energy when they move from a lower energy level to a higher one. This transition requires an input of energy as the electron must overcome the attractive force from the nucleus to reach a higher orbit. For instance, moving from the second to the fourth energy level absorbs energy, which can be visualized as climbing uphill.
  • Absorption occurs with transitions to higher energy states.
  • Energy addition can come from light or other forms of electromagnetic radiation.
Conversely, electrons emit energy when they fall from a higher energy level to a lower one. This emission releases energy because the electron moves closer to the nucleus, revealing a loss of potential energy, similar to sliding downhill. This energy is released often in the form of light.
  • Emission happens during transitions to lower energy states.
  • Light energy is often emitted as photons during these transitions.
Grasping these concepts of absorption and emission is crucial for understanding how spectral lines are created and why each element has its unique emission spectrum.
Principal Quantum Numbers
The concept of principal quantum numbers is fundamental to quantum mechanics and atomic physics. In the hydrogen atom, each electron occupies a unique energy level or orbit, characterized by the principal quantum number, denoted as \(n\).

This quantum number not only defines the size of the orbit but also its energy, as energy levels increase with \(n\). Lower \(n\) values refer to orbits closer to the nucleus, while higher values indicate orbits further out. For instance, \(n=1\) represents the smallest orbit, which is closest to the nucleus and has the lowest energy.
  • The principal quantum number \(n\) dictates the electron's orbital size and energy.
  • Lower \(n\) signifies orbits near the nucleus with less energy.
  • Higher \(n\) values relate to orbits that are larger and carry more energy.
Each increase in \(n\) signifies a significant step up in energy level, and while electrons need energy to move to a higher \(n\), moving to a lower \(n\) results in energy emission. Familiarizing yourself with this number allows a deeper understanding of electron configurations and the size of atoms.
Hydrogen Atom Electron Transitions
Electron transitions within a hydrogen atom involve movement between specific energy levels, dictated by quantum rules. These transitions can be predicted using the principal quantum number and are key to understanding atomic spectra and energy exchanges.

In practical terms, when an electron in a hydrogen atom transitions from one orbit (defined by \(n_i\)) to another (defined by \(n_f\)), energy changes are calculated. The transition formula \(\Delta E = E_f - E_i\) helps determine if the energy is gained or lost.
  • Transiting from a higher \(n\) to a lower \(n\) emits energy.
  • Moving from a lower \(n\) to a higher \(n\) absorbs energy.
These transitions are central to the production of spectral lines and the emission of light when electrons drop to lower energy states. Observing hydrogen spectrum lines involves detecting photons released during such transitions, a foundational principle in spectroscopy. Understanding these transitions enables insight into atomic structure and physicochemical behaviors, essential for both chemistry and physics.

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Most popular questions from this chapter

In the television series Star Trek, the transporter beam is a device used to "beam down" people from the Starship Enterprise to another location, such as the surface of a planet. The writers of the show put a "Heisenberg compensator" into the transporter beam mechanism. Explain why such a compensator would be necessary to get around Heisenberg's uncertainty principle.

Which of the quantum numbers governs (a) the shape of an orbital, (b) the energy of an orbital, (c) the spin properties of the electron, (d) the spatial orientation of the orbital?

The first 25 years of the twentieth century were momentous for the rapid pace of change in scientists' understanding of the nature of matter. (a) How did Rutherford's experiments on the scattering of \(\alpha\) particles by a gold foil set the stage for Bohr's theory of the hydrogen atom? (b) In what ways is de Broglie's hypothesis, as it applies to electrons, consistent with J. J. Thomson's conclusion that the electron has mass? In what sense is it consistent with proposals that preceded Thomson's work, that the cathode rays are a wave phenomenon?

The series of emission lines of the hydrogen atom for which \(n_{f}=3\) is called the Paschen series. (a) Determine the region of the electromagnetic spectrum in which the lines of the Paschen series are observed. (b) Calculate the wavelengths of the first three lines in the Paschen series - those for which \(n_{i}=4,5\), and 6 .

If you put 120 volts of electricity through a pickle, the pickle will smoke and start glowing an orange-yellow color. The light is emitted because the sodium ions in the pickle become excited; their return to the ground state results in light emission (see Figure \(6.13 \mathrm{~b}\) and Sample Exercise 6.3). (a) The wavelength of this emitted light is \(589 \mathrm{~nm}\). Calculate its frequency. (b) What is the energy of \(0.10\) mole of these photons? (c) Calculate the energy gap between the excited and ground states for the sodium ion. (d) If you soaked the pickle for a long time in a different salt solution, such as strontium chloride, would you still observe \(589 \mathrm{~nm}\) light emission? Why or why not?

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