Chemistry lab
Models of the Hydrogen Atom[footnoteRef:1] [1: Adapted from PHET Interactive Simulations and an activity by Trish Loeblein, University of Colorado, Boulder. This lab requires use of a computer running Microsoft Windows or OS X 10.9.5 or later with internet access.]

Objectives
· Visualize and describe different models of the hydrogen atom.

· Explain the predictions from each model of the hydrogen atom.

· Explain energy levels of electrons in the hydrogen atom.

Background Information
John Dalton proposed that each element is a tiny, indestructible particle called an atom. Dalton’s idea was that atoms of a given element have properties that distinguish them from of other elements. This lab will call Dalton’s model of the atom the Billiard Ball Model because billiard balls have properties that distinguish them from each other – color and pattern.

The Plum Pudding Model of the atom based on work by J. J. Thomson and Robert Millikan who separately showed negatively charged, small electrons can be “chipped” from the atom. So, based on their observations, the atom looks like a plum pudding – dried fruit held together by a custard or a mousse.

Just like the fruit can be “chipped” from the pudding, in the Plum Pudding Model electrons can be “chipped” from the atom. If electrons are negatively charged particles, the pudding must be a positively charged “sphere or cloud” to balance the difference between the charge on the electron and the rest of the atom.

Niels Bohr proposed the Bohr Model of the atom to explain how the structure of the atom changes when it undergoes changes in energy. Bohr’s idea was that the energy levels in an atom are quantized and that the amount of energy in the atom is related to the electron’s position in the atom. Quantized energy levels mean that the atom has specific amounts (levels) of energy. If the energy is quantized, the electron’s position in the atom is quantized as well.

In the Bohr Model, electrons in an atom are organized into discrete energy levels described as fixed circular orbits of the electron around the nucleus. The farther the orbit is from the nucleus, the higher the energy level.

The Schrödinger Model of the atom is based on work in Quantum Mechanics by famous scientists including Max Planck, Albert Einstein, Erwin Schrödinger, Werner Heisenberg, Max Born and others. In the Schrödinger Model, a dense nucleus makes up more than 99% of the atom’s mass and the electrons are dispersed in a cloud around the nucleus. Like the Bohr model, energy levels of the electrons are quantized, but in the Schrödinger model, energy levels of the electrons are split into several sublevels (aka subshells). Sublevels contain electron clouds in three dimensional shapes called orbitals.

Procedures
Part 1. Experimental Observation of Photons Beamed Through a “Box” of Hydrogen Atoms

1. Record observations answers to questions in these instructions. Questions must be answered completely with applicable scientific terms and concepts.

2. Download and Open the Simulation of “Models of the Hydrogen Atom” From Canvas or the PHET website: (https://phet.colorado.edu/sims/cheerpj/hydrogen-atom/latest/hydrogen-atom.html?simulation=hydrogen-atom

3. Make sure “Experiment” is highlighted white.

4. Turn the light beam “on.” Photons of different wavelengths (colors) flow from bottom to the top of the simulation.

5. Turn “Light Controls” to white.

6. Check the Show Spectrometer box next to the “Light Controls”.

7. Adjust the speed of the photons with the slider at the bottom of the simulation to fast and observe what happens while photons are being sent through a box of hydrogen atoms for at least 4 minutes.

8. What are the two things the spectrometer is recording?

i. :

ii. :

9. When determining how an atom works, scientists observed something like what you are observing now and proposed how the atom must be organized.

a. What do you observe about the color of the photons and about how many photons (intensity of lines in the visible spectrum) that are “deflected” from the box of hydrogen?

b. What do you think is making the photons “deflect” from the box of hydrogen atoms? Provide your own hypothesis.

Part 2. Understanding Different Models (Theories) of the Hydrogen Atom

10. Now that you have provided a hypothesis about what is happening to the photons, highlight the “Prediction” button and observe results of predictions from each model of the hydrogen atom.

Observe results of predictions from a “monochromatic” wavelength of 97 nm and results from white light. Record observations about photons, observations from the spectrometer and the energy level diagram.

· Note: The energy level diagram is not available in the Billiard Ball and Plume Pudding Models.

Observe for at least four minutes with fast and slow photon settings.

Complete the tables below.

a. Complete Observations of Predictions (what the model predicts) from the 4 models.

· Reset the spectrometer in between each model.

Atomic Model

Observations of Predictions (what the model predicts)

97 nm

White light

Billiard Ball

Plum Pudding

Bohr

Schrodinger

b. Explain how each model’s predictions do or do not explain the experimental observations.

Atomic Model

How does the model explain or not explain the experiment observations?

Billiard Ball

Plum Pudding

Bohr

Schrodinger

Part 3. Explain Details of Bohr’s Model of the Hydrogen Atom

11. With the Bohr’s model selected, click the “Show electron energy level diagram.”

12. Using information from the Electron Energy Level Diagram and the Spectrometer, describe in detail what is happening to the one electron in hydrogen as white light (continuous) photons are absorbed by the hydrogen atom.

This is more easily done with “slow” photons, takes time, and careful observation. You have three things to watch and interpret:

i. the n = 1,2,3… levels shown in the box on hydrogen

ii. the Energy Level Diagram

iii. information from the spectrometer.

Detailed description:

13. In the help menu, click on transitions. Enter each of the first 5 wavelengths into the wavelength box and describe what happens to the electron for each wavelength. This will take some time, especially for 94 nm wavelength.

Wavelength (nm)

Observations: what happens to the electron?

122

1 ? 2

103

1 ? 3

97

1 ? 4

95

1 ? 5

94

1 ? 6

14. Which one wavelength from #13 produces the same emission spectrum with the same wavelengths as the emission spectrum from white light? Explain why the one wavelength does produce the same spectrum as from white light and the other four wavelengths do not produce an emission spectrum. Hint: consider how different wavelengths are produced in an emission spectrum.

15. Do observations from steps #13 and #14 support your ideas in #9? If not, readjust your statement to explain you new ideas about the behavior of the electron.

16. Now enter one wavelength that is not listed in the help menu under transitions. What do you observe? Does this support your ideas? Explain.

17. What did you learn from this lab?

18. Extra Credit: Explain what is happening in the Planetary model and de Broglie model simulation predictions of the hydrogen atom.

Finished Lab Report – Submit on Canvas

Submit your completed lab report (these instructions) on Canvas as a single pdf file.

Neatness counts toward your report score.

Instructions: Models of the Hydrogen Atom Page 5