Simulation: Hydrogen Atom

Regarding the example on the previous page, to simulate the transition and see the dark line spectrum, open the "Hydrogen Atom" then follow the instructions below.


On the simulation, select "View Calculations" and press "play".  Next, select the n = 3 transition.  Check to see if these results match the results from the previous example.

Using this simulation, see if you can verify each of the points below, summarizing the Bohr Model of the atom.


Summary of the Bohr Model

  • Absorption (nf > ni).  When an electron "jumps" to a higher energy level, it must absorb energy.  Each transition requires a specific amount of energy.  The dark lines in an absorption spectrum correspond to specific photon wavelengths that are needed for an electron to jump from lower to higher energy levels.

  • Emission (nf < ni).  When an electron "falls" to a lower energy level, energy is emitted.  Each transition emits a specific amount of energy.  The lines that are seen in an emission spectrum correspond to specific photon wavelengths that are emitted when an electron falls from higher to lower energy levels.
     
  • Absorption and emission lines match.  For example, the magnitude of the change in energy (ΔE) when an electron rises from n = 1 to n = 2 is equal to the magnitude of the change in energy (ΔE) when an electron falls from n = 2 to n = 1.
     

  • The absolute value, or the magnitude of the change in energy, is calculated based on the initial and final energy of the electron that undergoes a transition:

  • The frequency or wavelength of an absorbed or emitted photon can be calculated with .


Read
Read "The Bohr Model of the Atom" on pages 773 to 780 of your physics textbook.



Absorption spectrum: a pattern of dark lines produced when light passes through a gas at low pressure.



Emission spectrum: a pattern of bright lines produced by a hot gas at low pressure


Test your understanding of Bohr's model of the hydrogen atom by answering the following questions.  When ready, click the "Check your work" bar to assess your responses.

SC 3. Review the assumptions Bohr made.  Which of these assumptions "fit" with classical physics and which support the ideas of quantum physics?

SC 4.  Sample equipment to show atomic absorption lines is shown in the diagram below.  Absorption lines occur in atomic spectra when an electron absorbs energy.  The electron quickly drops back to the ground state, releasing a photon with the same amount of energy that was absorbed.  If the photon is released, why doesn't it show up on the atomic spectra?

 

Contact your teacher if your answers vary significantly from the answers provided here.

SC 3. 

Postulates That "Fit" Classical Physics

Postulates That "Fit" Quantum Physics
  • Electrons orbit the nucleus. They are held in orbit by an electrostatic force.
  • Electrons can only be in certain, permitted orbits and an electron does not emit radiation when it is in one of these orbits.
  • An electron only emits radiation when it "falls" from a higher energy state to a lower state.

 

SC 4.  The initial incident photons are all projected in one direction through the atomic gas and onto the detector or screen. The photon absorbed by the electron and later released is scattered in a random direction, as shown in the diagram below. As a result, the dark lines are a very few photons re-emitted in that direction but the majority of the photons are emitted in different directions.


Try This
Use the Bohr Model of Hydrogen Simulation (you will need to use Firefox) to shoot a stream of photons through a container of hydrogen gas.  Observe how photons of certain energies are absorbed, causing changes in the orbits of electrons.  Build the spectrum of hydrogen based on photons that are absorbed and emitted.


Try This
Use the Bohr Model: Introduction Simulation to fire photons and observe how an absorbed photon changes the orbit of an electron and how a photon is emitted from an excited electron.  Calculate the energies of absorbed and emitted photons based on energy level diagrams.  The light energy produced by the laser can be modulated, and a lamp can be used to view the entire absorption spectrum at once.