# Experiment 7 Atomic Spectroscopy - PowerPoint

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```					              Experiment 7
Atomic Spectroscopy

Valdosta State University
Goal

To calculate the Rydberg constant from experimental data
and observe the characteristic colors of some metal salts
when burned.

Valdosta State University
Background – Emission Line Spectra

Valdosta State University
Background – Emission Line Spectra
Transitions that may
Excitation          emit light

Excited States                            Light

Light

Ground State
state

Figure 1

Ground state – an electron in its lowest possible energy orbital.
Excited state – an electron which gains energy from an outside source and
moves into an higher energy orbital.

Valdosta State University
Background – Emission Line Spectra

Valdosta State University
Background – Rydberg

1         1   1 
  RH  2  2 
        n      
 i nf 

 = wavelength
RH = Rydberg constant
ni = principal quantum number of the excited state
nf = principal quantum number of the final state

Valdosta State University
Background – Line Spectra
In order to determine the value of the Rydberg constant,
the Rydberg equation must be rearranged.

1         1          1 
  RH  2
n      RH  2 

                      n 
 i          f 

Valdosta State University
Background – Line Spectra
In order to determine the value of the Rydberg constant,
the Rydberg equation must be rearranged.

1         1              1 
  RH  2
n          RH  2 

                          n 
 i              f 
Now, assume that the electrons always relax back to the
same energy level.
 1 
- this means that  R  n  is a constant or “c”
H    2
f

1         1    
  RH  2
n     c

         i    

Valdosta State University
Background – Line Spectra
1         1   
  RH  2
n    c

         i   

This equation is now in the slope-intercept form or
y = mx + c
So, if we plot
1                       1   
as y and              2
n    
   as x
                       i   

The slope of the line should be –RH
RH
The Y-intercept of the line =
n2
f
Valdosta State University
Technique - Project Star Spectrometer

Valdosta State University
Technique - Project Star Spectrometer

Valdosta State University
Technique - Project Star Spectrometer

Valdosta State University
Technique – Flame Test

Valdosta State University
Technique – Flame Test

1.     Collect a small amount of salt in a semi-micro
scoopula.

Valdosta State University
Technique – Flame Test

2.     Place scoopula in the hottest part of a bunsen burner
flame.

Valdosta State University
Technique – Flame Test

3.     Observe and record the color of the flame.

Valdosta State University
Calculations – Line Spectra
The following lines can be observed for hydrogen:
Wavelength (approx)            Color
440 nm                   purple
480 nm                   blue
650 nm                   red

Valdosta State University
Calculations – Line Spectra
The following lines can be observed for hydrogen:
Wavelength                Color
440 nm                   purple
480 nm                   blue
650 nm                   red

Wavelength                 (Wavelength)-1
440 nm  4.40 x 10-5cm          22727 cm-1
480 nm  4.80 x 10-5cm          20833 cm-1
650 nm  6.50 x 10-5cm          15385 cm-1

Valdosta State University
Calculations – Line Spectra

• The values of ni are determined by trial and error
– Plot several sequential series of ni, your answer will be the
series that yields a value closest to the Rydberg constant.
• n = 2, 3, 4           Lyman series
• n = 3, 4, 5           Balmer series

Valdosta State University
Calculations – Line Spectra
24000

22000
wavenumber (cm )
-1

20000

y = -105896x + 27223                          y = -39608x + 25276
18000                               R2 = 0.9972                                  R2 = 0.9999

16000

14000
0           0.05        0.1                    0.15           0.2                  0.25
2
1/n

n=2,3,4   n=3,4,5             Linear (n=2,3,4)   Linear (n=3,4,5)

Valdosta State University
Safety

• Do not look directly in to the gas discharge tubes for
extended periods of time.

Valdosta State University
Waste Disposal

• Place all unused salts in the waste bottle labeled:
“Recovered Metals and Metal Ions”

Valdosta State University
Advising

• Registration for Summer and Fall 2007 begins March 26,
2007
• Check in the main department office (of your major) to
see who is your advisor.
• Please keep in mind that the faculty member who
advised you during orientation may not be your
permanent advisor.
• Do NOT wait until the last minute to get advised.
• You will NOT be able to register until you have been
advised and your advisor has lifted your “flag”.

Valdosta State University
Other reminders

• Midterm (i.e. last day to withdraw from classes) is March 2, 2007.
• If you decide to drop the lecture, you do NOT need to drop the lab.
However, if you wish to drop one but not the other, you CANNOT
withdraw on the web; you need to actually get the form from the
registrar and get the signature of the instructor. You only need the
signature of the laboratory instructor, you do not need my signature.
• Also, registration begins on March 26, 2007.
• Be sure to see your advisor in order to have your “flag” lifted so you
are eligible to register
• If you do not know who your advisor is, please see the department
of your major

Valdosta State University
Important Reminders - Prerequisites

• In order to take CHEM 1212 and CHEM 1212L, you
need to meet the following prerequisites:
• MATH 1111 or MATH 1113
• CHEM 1211
• CHEM 1211L
• In all courses, you MUST have a grade of “C” or better.
• Even though the system may let you register, we will be
checking the grades at the end of the semester to
ensure that all students registered for CHEM 1212
and/or CHEM 1212L have good enough grades.
• If you do not have the grades, you will not be allowed to
remain in CHEM 1212 AND CHEM 1212L courses in
Summer or Fall 2007.

Valdosta State University

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