Color, Light, and Excited Electrons

Lorna Paisley                  Lincoln-Way High School
                               1801 East Lincoln Highway
                               New Lenox IL 60451
                               (815) 485-7655

Objectives:

Grade Level:  Various parts for various levels.
The Students will be able to:
A. Understand what a wave is.
B. Identify wave parts - crest, frequency, wavelength, trough.
C. Recognize visible light as part of the electromagnetic spectrum. 
D. Understand the continuous spectrum (the rainbow) of visible light - that 
   different wavelengths of light produce different colors. 
E. Understand how color helps identify elements and that it is excited electrons 
   that produce this color.
F. Understand how excited electrons are used for toys, entertainment, by nature,   
   in the business world, in lighting, etc.
G. Have some understanding of and recognize the differences among luminescence, 
   chemiluminescence, fluorescence, and phosphorescence.

Materials Needed:
 
To produce waves:  a slinky or a rectangular plastic pan (#6 plastic pastry pan) 
and a 1 inch dowel rod or some workable stick. 

To produce a continuous spectrum or rainbow:  overhead with all light blocked 
but one thin strip and a prism or prism glasses.  Or just use prism glasses on 
an individual basis. 

To illustrate an excited electron giving off light:  Confetti, desk and table of 
different heights. 

To show element identification:  wood splints, sodium chloride (table salt), 
potassium chloride (salt substitute), copper sulfate (root killer from nursery), 
strontium nitrate, calcium nitrate, barium nitrate, lithium nitrate.  Nitrate 
compounds must be purchased from chemical supply companies.  Spectrum power 
supply and gas spectrum tubes of gaseous elements. 

To demonstrate luminescence:  Prestone antifreeze, beaker or glass jar, 
overhead, blacklight, detergent samples, light sticks, and other fluorescing 
materials. 
 
Strategy:

Activity 1:  Diagram a wave on the board.  Label the wavelength, crest, and 
trough.  Use the slinky to make waves on the floor.  Point out the crest, trough, 
and wavelength.  Explain that frequency is the number of crests that pass a given 
point in a given amount of time.
Show how energy affects wavelength and frequency.  Have 1 student keep track of 15 
second intervals.  Have another student keep track of the number of peaks that 
pass him/her during this time interval.  The teacher can make waves, using 
little energy, that have a large wavelength and low frequency.  Then she can use 
more energy and make waves that have a small wavelength and a high frequency. 

Activity 2:  To explain the fact that electrons are confined to certain 
orbitals, you become the electron and stand on the floor.  Then add energy by 
having someone shine a light on you or by eating a candy bar and then climb up 
on the chair, which is a higher energy level.  Then add more energy and climb up 
on the desk, an even higher energy level.  Then, to explain that electrons 
return to the ground state, jump down.  Because energy is given off, throw out a 
handful of confetti at one of the levels.  This confetti represents visible 
light.  At one of the jumps they see no light because the energy given off is 
ultraviolet or infrared.   

Activity 3:  To identify elements by the flame color, soak a splint in a 
distilled water solution containing a compound of the element for several  
hours.  Heat, but do not burn, the splint in a hot flame for the identifying 
color.  Each element will produce a different colored flame.  To identify 
gaseous elements use the spectrum tube power supply, the spectrum tubes, and 
diffraction gratings or rainbow glasses.  Students can see that each gaseous 
element produces a different "atomic" spectrum.  Different parts of the rainbow 
are present for each element. 

Activity 4:  To demonstrate the 3 types of luminescence: fluorescence, 
phosphorescence, and chemiluminescence, begin with a light stick.  Follow 
directions on the package to show chemiluminescence.  To demonstrate 
phosphorescence use sunlight or a black light.  Both are sources of ultraviolet 
light.  Shine the light on a T-shirt or key chain with glow in the dark 
properties.  To show how industry uses fluorescence turn out the room lights, 
turn on the black light and display soaps and detergents and sales tags.  Many 
of them fluoresce for better visibility.  Have students bring in boxes and 
bottles from home to see if they fluoresce.  You can also show fluorescence of 
the soaps and detergents by rubbing them on your hands or clothing.  Prestone 
Antifreeze, placed in a beaker and set on the overhead will also show this. 

Performance Assessment:             

Assess understanding of waves and movement of electrons by having students draw 
diagrams and label the parts or movement.  Have students make a list of the 
colors of the spectrum and in the ROYGBIV order.  Assess element identification 
by having each student identify an unknown element.  The three types of 
luminescence can be assessed by having students give an example of each.