Name _________________________
Partner’s Name(s) _________________________
Excited Elements - Light Emission Spectroscopy
Introduction:
As electrons absorb energy they become excited and move to higher energy levels. As the electrons fall back to
lower energy levels they release the energy they absorbed in set amounts called quanta. The energy that is
released as electrons fall from higher to lower energy levels has a characteristic wavelength and frequency that
corresponds to a particular type of electromagnetic radiation. For example, when electrons fall from a higher
energy level down to the 2nd energy level, the wavelength and frequency of the energy produced correspond to that
of visible light.
Electrons of atoms can be excited in various ways including heat, electricity and friction. For example, a solution of
sodium chloride placed on a platinum wire and held in a flame emits a bright, yellow light that is characteristic of
the metallic element sodium. Another method of spectrum analysis involves the application of high voltage across a
gas-filled glass tube. Gases under low pressure and excited by an electrical discharge give off light in characteristic
wavelengths. The emitted light is passed through a spectroscope, which breaks light into its components for
analysis. A gas viewed through a spectroscope, such as the one shown in Figure 1, forms a series of bright lines
known as a bright-line or emission spectrum. Since each element produces a unique bright-line spectrum or
pattern, spectroscopy is a valuable branch of science for determining what elements are present. The composition
of stars and other objects in outer space is determined using this technique. Unlike gases, heated solids produce a
continuous spectrum.
A gas is identified by comparing the wavelengths of its emission (bright line) spectrum to the spectrum produced
by a known gas. In this experiment, you will use a spectroscope to determine the bright-line spectra characteristic
of different elements.
Purpose:
To observe the characteristic bright line spectra produced by applying high voltage across a sample of a
gas at very low pressure and to determine the identity of an unknown gas.
Materials/Equipment:
High voltage power supplies
Diffraction grating glasses
Spectroscopes
40-watt incandescent bulb/socket
Thermal mitt
Fluorescent bulb/socket
Colored Pencils (ROY G. BIV)
Label Cards for each spectral tube
Spectral tubes:
Helium
Neon
Oxygen
Mercury
Nitrogen
Hydrogen
Unknown
Safety Considerations:
 DO NOT TOUCH the spectrum-tube power supply or spectrum tubes when power is applied.
Several thousand volts exist at the power supply and spectrum tubes.
ASIM Spectrophotometry: Excited Elements
Revised: 6/06
p. 1
Name _________________________
Partner’s Name(s) _________________________
Procedure:
1. Obtain a spectroscope and look through it at an incandescent light bulb. The spectrum should appear
when the slit in the spectroscope is pointed just off center of the glowing filament. Practice moving
the spectroscope until you see a bright, clear image.
2. Darken the room but leave enough background lighting to illuminate the spectroscope scales. Point
the spectroscope away from any exposed window, since daylight will affect the observed gas
spectrum.
3. Helium or hydrogen is a good first choice among the spectral tubes set up around the room. Adjust
the spectroscope until the brightest image is oriented on your scale. Record in Table 1 the five
brightest lines of the observed spectrum. Some of the spectrum tubes produce light so dim that you
must be very close to them to get good observations of the spectral lines.
4. Repeat for each of the other spectrum tubes.
Figure 1: Look through the spectroscope at the emitted light of the spectrum tubes.
ASIM Spectrophotometry: Excited Elements
Revised: 6/06
p. 2
Name _________________________
Partner’s Name(s) _________________________
Data: Draw in lines at the proper locations and of the correct width and intensity to reflect what you have
observed. On the line at the right of each scale, write the name of the element you are observing.
Sketch of line spectrum
O2
V
I
B
G
Y
O
R
Y
O
R
Y
O
R
Y
O
R
Y
O
R
Y
O
R
Sketch of line spectrum
N2
V
I
B
G
Sketch of line spectrum
Ne
V
I
B
G
Sketch of line spectrum
Hg
V
I
B
G
Sketch of line spectrum
H2
V
I
B
G
Sketch of line spectrum
He
V
I
ASIM Spectrophotometry: Excited Elements
Revised: 6/06
B
G
p. 3
Name _________________________
Partner’s Name(s) _________________________
Questions:
1. How do electrons respond when energy is added?
2. When materials are heated, or receive energy, their electrons ______________________.
3. The color of the light is characteristic of the ____________________________________.
4. Every element has its own pattern of emitted light…a
.
5. We can look at this pattern through a
.
6. Light passes through a slit, then through the grating and separates into
.
7. This is called a/an
.
8. This method is used by astronomers to determine the composition of the
.
9. What produces the color of fireworks?
10. Explain how it is possible for colored “neon lights” to be changed to reflect the colors of a specific
product (advertisement signs) or to enhance the appearance of a business sign.
11. Are all the lines of the spectral patterns of the same intensity? Explain.
12. Are they always in the same order: ROYGBIV? Explain.
13. Why are the lines different colors?
Applications:
1. Describe the uses of a spectroscope in the science of astronomy.
2. How can spectra be used in chemical analyses?
ASIM Spectrophotometry: Excited Elements
Revised: 6/06
p. 4