Composition of the Atom

Carol Zimmerman                Lane Tech High School
                               2501 W. Addison St.
                               Chicago IL 60618
                               312-534-5400

Objectives:

1. This lesson is for High School.

2. The students will become familiar with the following vocabulary:
   atom          proton          neutron         electron        hadron
   nucleus       quark           lepton          probability     wave
   charge        mass            muon            pion            strong force
   weak force    vector boson    gluon           graviton        Higg's boson

3. The students will be able to construct a model of the atom for any element.
   A performance assessment will be made of this task.

Materials Needed:

Class
     beaker      water           ethyl alcohol          motor oil
     small pointed stick               food coloring (optional)
     periodic table of the elements

Group of four
     sheet of paper filled with circles                  
     gumdrops    toothpicks      calculator

Individuals
     gumdrops    toothpicks      calculator        wave line

Strategy:

     Define the words: proton, electron, neutron, nucleus.  Pass out copies of 
the periodic table of the elements and put one enlarged element on the board or 
the overhead.  Review the recognition of the atomic number and atomic mass and 
how one would use them to determine the number of protons, neutrons, and 
electrons in the rest atom. 

     Have the class discuss perceptions of normal behavior of positively and 
negatively charged particles.  To demonstrate the effect of the strong force in 
the nucleus:  Fill a beaker half full of water.  Float a layer of ethyl alcohol 
on the top of the water.  Add one or two drops of motor oil.  It will remain 
suspended between the water and the alcohol.  (If you wish this to appear to be 
magic, add the alcohol to the water out of the students' sight.  If you want the 
students to be aware of the two different layers, add a small amount of food 
coloring to the water before adding the alcohol.)  Poke at the oil bubble with 
the stick and notice how it resists splitting.  Relate this to the strong force 
in the atom. 

     Pass out one sheet filled with circles to each group of four students.  
Have each student in the group drop a pen or pencil, point down, from waist 
height 25 times.  The students will count the total number of marks that have 
landed inside any of the circles.  Using the ratio :   

           area of all of the circles = dots inside any circle
           area of the sheet of paper            100 dots

Find the area of all of the circles.  Divide this number by the total number of 
circles to find the area of one circle.  i.e.

                  area of all of the circles = area of one circle
                      number of circles

Use the formula:         A=pi*r2 
to find the radius and the diameter of one circle.  Relate this to Rutherford's 
experiments to find the size of the nucleus.  Explain that to be completely 
parallel there would be only one or two circles on the page, but that then you 
would need at least 500 to 1000 drops of the pencil to get an adequate sampling. 

     Discuss electron orbits, including energy levels, probability theory, and 
the formula for the maximum electrons in an orbit: 2n2.  Have each group 
construct a model of a helium atom, using toothpicks and gumdrops.  Color code 
the atom, using a different color for protons, neutrons, and electrons.  

     Introduce wave theory.  Explain that each element has a unique wavelength k 
associated with it.  Then for each energy level n, the circumference can be 
found by the formula: 
                           circumference = nk

     Introduce modern physics by explaining that the word modern is extremely 
relative.  Any music more recent than the nineteenth century composers Verdi and 
Wagner is considered modern.  A turn-of-the-century Picasso painting is modern 
art.  In physics, nothing older than yesterday is classified as modern.  Twenty 
years ago scientists thought that an atom was composed of hadrons (protons, 
neutrons, and pions), and leptons (electrons, neutrinos, and muons).  Ten years 
ago they were saying that hadrons were composed of quarks, of which there were 
three different types.  At this point you might bring up the origin of the word 
quark.  It was taken from the line "Three quarks for Muster Mark." from the 
James Joyce novel Finnegan's Wake.  In German there are two translations of the 
word: the conventional "cottage pudding" and the colloquial "strange".  By five 
years ago the scientists recognized six kinds of quarks.  The up, charm, and 
truth (or top) each have a charge of +2/3.  The down, strange, and beauty (or 
bottom) each have a charge of -1/3.  In addition, quarks have the "colors" of 
red, blue, and green.  Since quarks only exist in a high energy state, their 
mass is actually greater than the rest mass of the hadrons they compose.  In 
addition to hadrons and leptons, atoms also contain vector bosons (the W and Z 
particles and gluons) which are associated with the strong force which binds the 
nucleus together, gravitons, and the Higg's boson. 

Performance Assessment:
            
     Using their copy of the periodic table of the elements, gumdrops, 
toothpicks, a model wave three wavelengths long, and a calculator, each student 
will construct a correct model of the magnesium atom. 


Scoring Rubric:

                     BUILDING AN ATOM

                  Demonstrated Competence

6 - Exemplary Response
     The numbers of protons, neutrons, and electrons are correct.
     The number of electrons in each orbit is correct.
     The circumference of each orbit is correct.
     There is appropriate scientific justification for all of the above.

5 - Correct Response
     The numbers of protons, neutrons, and electrons are correct.
     The number of electrons in each orbit is correct.
     The circumference of each orbit may not be correct.
     There is no scientific justification for any of the above.


                   Satisfactory Response

4 - Almost Correct Response
     The numbers of protons, neutrons, and electrons are correct.
     The number of electrons in each orbit is not correct and/or there is no 
     mathematical explanation for that number.
     The circumference of each orbit is incorrect.

3 - Partial Solution
     The numbers of either the protons, neutrons, or electrons is incorrect.  
     The other two are correct. 
     

                    Inadequate Response

2 - Inadequate Solution
     The numbers for either the protons, neutrons, or electrons is correct.  The 
     other two are incorrect. 
     
1 - Incorrect Response
     The numbers of protons, neutrons, and electrons are all incorrect.

0 - The student leaves a blank page or writes "I don't know".