Subatomic Particles and Light: A Study of Electron Energy Levels

Procedures

Even though an atom is very tiny, there are even smaller particles that make up an atom.  These subatomic particles are in specific locations in the atom.  The protons, (+) charged particles, and the neutrons, neutral particles, exist in an inner core of the atom called the nucleus.  The electrons, (-) charged particles, reside in well-defined energy shells around the nucleus call orbits.  

Light is used to study electrons.  Light, or electromagnetic (EM) radiation, has different properties depending on the energy.  For example, EM radiation with high energy (such as gamma and x-rays) have very short wavelengths.  EM radiation with low energy (microwaves and infrared) have long wavelengths.  Energy and wavelength are inversely proportional; if you increase one, the other will decrease.  For visible light, red has long wavelengths (low energy) and violet has short wavelengths (high energy).  

Electrons are not confined to a certain shell in the atom.  In fact, the electrons can absorb energy from a flame or a spectrometer (a spectrometer provides light energy at very specific wavelengths) and jump to a higher energy shell.  They can also relax back to the original shell and emit energy in the form of light.  They only emit certain colors of light depending on the location of the energy shells. 

A. Flame Test 

1.Set up the Bunsen burner as demonstrated by your lab instructor.  Make sure you have the proper flame height and input of oxygen.

2.Obtain a copper loop and a solution of strontium chloride.

3.Dip the copper loop into the strontium chloride and carefully place the loop into the flame.

4.Record your observations on your report sheet.

5.Repeat steps 3 and 4 with samples of barium chloride, calcium chloride, and copper (II) chloride.

B. Absorption of Colored Compounds 

1.You will be measuring the absorption of one of the colored solutions provided in lab today.  Each group will be measuring a different colored solution and the data will be compiled at the end.

2.Your instructor will demonstrate the use of the spectrometer.

3.Obtain two, clean, dry, test tubes.  Use caution in handling the test tubes.  Use a Kimwipe to wipe the outside of the test tubes and avoid
leaving fingerprints on the outside.

4.Fill the first test tube near the top with your colored solution.

5.Fill the second test tube with distilled water.

6.Set the spectrometer to 400 nm (NOTE if your sample is green or violet, start making measurements at 460 nm.  For the other colors (red,
orange, yellow, and blue) start at 400 nm).

7.Make sure the filter (the bottom left lever) is set to the 400-599 nm range.

8.With an empty spectrometer, set the transmittance to 0% using the front, left, knob.

9.Insert the test tube filled with water into the spectrometer.  Set the transmittance to 100% using the front, right, knob.

10.Change the spectrometer reading from Transmittance to Absorbance using the white button by the digital display.

11.Insert your sample into the spectrometer and record the absorbance.

12.Increase the wavelength to 420 nm.  Insert the water sample back into the spectrometer and set the transmittance to 100% (change the spectrometer reading back to transmittance using the white button).

13.Insert your colored sample back into the spectrometer and record the absorbance.

14.Repeat steps 7 and 8 and increase the wavelength by 20 nm for each reading.  You will need to insert the water sample at each new wavelength and reset the transmittance back to 100%.

15.When you reach 599 nm, you will need to switch the range on the spectrometer.  This is the bottom, left, lever.

16.Make a graph of your data by plotting the wavelength on the x-axis and the absorbance on the y-axis. The individual data is provided for you in the lab module.  All six of the colors are provided.  You will only need to choose one color to make your plot.  Pick a color and fill in the Report Sheet for part B.  Make sure you include the color you chose.

17.Determine the wavelength of maximum absorbance (the wavelength that corresponds to the largest y-value).

18.Record your value on your report sheet and place your results in the “Class Data” section.

19.Use the chart to determine the color of your maximum absorbance and the wavelength of your colored solution.

20.Use the remainder of the data to fill in the “Class Data” section.  You do not need to plot this data.  You can obtain the information you need by examining the absorbance values for each color.

1.What do you notice about the color of the solution and the wavelength of maximum absorption?  Does it correspond to the color of the sample?  What is the relationship between the two?

2.Define the following terms regarding the atom in your own words:

a.Electron shell

b.Absorption

c.Wavelength

d.Emission Spectrum

3.Draw and embed a lithium-7 atom (a lithium atom with 3 protons, 3 electrons, and 4 neutrons) using the Bohr Model (the solar system model).  Make sure your particles are labeled appropriately.  Choose an electron and show what happens to it when energy is absorbed.

4.You have an unknown compound.  You have determined it is either strontium carbonate (SrCO3) or copper (II) carbonate (CuCO3).  How can you determine the identity of the unknown compound?