Robert Hatch

SUBTOPIC:

 Atomic Structure

OBJECTIVES:

The students will:

1. understand how the theory of atomic structure has changed over time
2. learn that many people have contributed to our understanding of the atom
3. realize that matter is made of discrete units

Background Information 

Over 2000 years ago, the Greek philosopher, Democritus, conceived the idea of matter unable to be cut. He called these ultimate pieces of matter atoms. The idea of a discrete unit continues today; however, there is no proof of the particulate nature of matter. At the end of the 1800’s several discoveries (X-Rays, radioactivity, and electrons) were made which enhanced the ideas of atomic structure. Through activities with radioactive substances, students will gain information on the discreetness of matter. 

ACTIVITY #1:

Historical Views of Atomic Structure

           1 class period, with 2-3 additional library days 

PROCEDURE:

1. To help the student understand the changing views of atomic structure over time, use cooperative learning techniques in researching and reporting on a wide range of contributors.
2. Divide the class into study teams to research and report on one person from the list of names given. Encourage the use of visuals (posters, models, transparencies, etc.) and costuming (to reflect the era of the scientists) for the group presentation to the class. Reports should be two to three minutes in length.
3. It may be helpful to give a quiz on the material the day following the completion on the activity.

List of Contributors

Democritus Dimitri Mendelevev Niels Bohr Aristotle Wilhelm Roentgen J.J. Thompson Joseph Priestley Robert Milikan Ernest Rutherford Antoine Lavoisier Marie Curie James Chadwick Humphrey Davy Max Planck John Dalton Albert Einstein

ACTIVITY #2:

Atomic Structure Contributors

            30 minutes

PROCEDURE:

1. Using the above list of scientists, let students work in small groups of three or four to produce a crossword puzzle with clues obtained from the presentations. Have each completed puzzle copied for distribution to the class.
2. Students should complete at least two puzzles that were produced by groups other than their own. This can be completed as a homework assignment.
3. If simple name recognition is a objective, the list of names can be made into word searches either with or without a word bank.

ACTIVITY #3:

Photographic Evidence of the Nature of Matter

            1 class period

MATERIALS:  

BECQUEREL KIT CONTAINING 6 SUBSTANCES, 3 OF WHICH ARE LOW-LEVEL RADIOACTIVE SOURCES, POLAROID 107 BLACK/WHITE FILM PACK, POLAROID CAMERA FOR FILM DEVELOPING

Background info for Activity

In 1896, Henri Becquerel discovered that certain substances affected a photographic plate in the absence of light. The plate showed a light area under the substance which is called a radioactive element. By repeating this effect students will see that something happens during radioactive decay. (See The Restless Atom, by Alfred Romer for more information)

PROCEDURE:

1. Place the six boxes on the film pack and leave undisturbed for 72 hours.
   
A B C 

D E F 

2. After 72 hours develop the film without opening the shutter of the camera. There are eight pieces of film in the pack.
3. Place the pictures in sequence on poster board.
4. Discuss the possible causes of what is observed on the pictures.
5. The developed film shows that there are three areas of varying brightness at positions A, C, E.

ACTIVITY #4:

What Develops Film?

           30 minutes

MATERIALS:  

POSTER OF EIGHT PICTURES FROM ACTIVITY #1

PROCEDURE:

1. Using the following chart of substances contained in the Becquerel kit, determine by the process of elimination which substances caused the brightened areas on the film.
   Contents of Boxes

   Box Substance

   ---

   A Uranium, Sulfur, OxygenB Sodium, Sulfur, Oxygen

   C Uranium, Nitrogen, Oxygen

   D Sodium, Nitrogen, Oxygen

   E Thorium, Nitrogen, Oxygen

   F Sulfur

2. Students should discover that Uranium and Thorium cause film to be exposed.

ACTIVITY #5:

What Causes a Geiger Counter to Click

           1 class period

Background Information for Activity

Using the six boxes from the Becquerel kit, students are to determine if any of the substances cause a Geiger counter to click greater than can be accounted for by background radiation. Background radiation is around constantly, coming to us from both space and earth. Students will also discover which substance will cause the Geiger counter to click greater than background radiation.

MATERIALS:  

BECQUEREL KIT, GEIGER COUNTER (AUDIBLE OR WITH COMPUTER INTERFACE TO SERVE A S A RECORDER)

PROCEDURE:

1. Instruct students to perform the following procedure:
   1. take a background radiation count as a control for the experiment
   2. place each of the six boxes from the Becquerel kit in sequence at the same distance from the Geiger tube
   3. count the clicks over a set time period (for example, count for 15 seconds then multiply to get counts per minute)
   4. compare results obtained from boxes with each other and background control
   5. record results on table that follows:
      
SOURCE COUNTS PER MINUTEtrial 1 trial 2 trial 3 

BACKGROUND 

BOX A 

BOX B 

BOX C 

BOX D 

BOX E 

BOX F 

2. Students will find that only the substances that affect photographic film, Uranium and Thorium, cause a Geiger counter to click greater than be accounted for by background radiation.

ACTIVITY #6:

What Factors Affect the Intensity of Radiation?

           1 class period

MATERIALS:   

BECQUEREL KIT, GEIGER COUNTER, METER STICK, SHEET OF LEAD, DECK OF CARDS

PROCEDURE:

1. Instruct students to perform the following procedure:
   1. use only the boxes from the Becquerel kit that affected the film and Geiger counter (i.e. A, C and E)
   2. take a reading for A, C, and E (one at a time) at 5 cm from the Geiger tube for a control
   3. test the effect of distance on the count
   4. test the effect of shielding on the count
   5. test the effects of sample size on the count by using from two to ten boxes of the same substance stacked up.
   6. test the effect of the length of time exposed on the count
      
Results I (control at 5cm)SOURCE CLICKS PER MINUTE

BOX A

BOX B

BOX E
Results II (distance in cm)

SOURCE CLICKS PER MINUTE 

10cm 20cm 30cm 40cm 50cm 

BOX A 

BOX C 

BOX E 
Results III (shielding at 5 cm)

SOURCES CLICKS PER MINUTE lead 1 card 5 cards10 cards20 cards 

BOX A 

BOX C 

BOX E 
Results IV (sample size at 5 cm)

SOURCE CLICKS PER MINUTE

2 4 6 8 10 

BOX A 

BOX C 

BOX E 
Results V (time in minutes at 5 cm)

SOURCE CLICKS PER MINUTE

2 min 4 min 6 min 8 min 10 min 

BOX A 

BOX C 

BOX E


    

2. the factors that affect the intensity of radiation are proportional to the distance, amount of shielding, size of the radiation source, and time of exposure. Write statements to explain the relationship of each factor of radiation intensity.

Bibliography

Harber-Schaim, Abegg, Dodge, Kirksey & J.A. Walter. Introductory Physical Science. Englewood Cliffs, NJ: Prentice Hall, 1987.

Metcalfe, H.C., Williams, J.E. and J.F. Castka. Modern Chemistry. New York: Holt, Rinehart and Winston, Inc., 1985.

Romer, Alfred. The Restless Atom.