Chemistry – Development of Atomic Theory
John Dalton
Answer the questions below after visiting the following website:
http://staff.concord.org/~ddamelin/chemsite/c_AtomicTheory/Images/dalton_theory.jpg
1. What did Dalton imagine atoms were like? Describe using both complete sentences and
by sketching.
2. Based on our modern understanding of atoms, what was one big problem with Dalton’s
atomic model?
JJ Thompson
Answer the questions below after visiting the following videos:
https://www.youtube.com/watch?v=GzMh4q-2HjM
https://www.youtube.com/watch?v=UUpD62r2wq8
1. Describe what a cathode ray tube is and what it does.
2. Sketch and label the cathode ray tube as it appeared in the video.
3. What happens to the beam in a cathode ray tube when a magnet is brought near the tube
and beam?
4. What did Thompson discover using magnets and cathode ray tubes?
5. What model for the atom did Thompson propose after the discovery from the last
question? Sketch and label that model (use the internet or the classroom textbooks for this
one).
**While you are here, here is a video of a person that made his own cathode ray tube (it is more
complex than the ones we have examined): https://www.youtube.com/watch?v=5-Bco8KRpmU
Ernest Rutherford
Part I
Visit the following webpage and then answer a few questions about the image:
https://sakai.ithaca.edu/access/content/user/jkleingardner/Principles%20HTML%20slides/img/ch
1/GoldFoil.jpg
1. What was the name of the experiment Rutherford used in the image above?
2. Sketch and label the experimental setup Rutherford used in his atomic experiments.
3. What did Rutherford discover based upon the results of this experiment?
4. Sketch an updated model for the atom based upon the new information from Rutherford’s
experiments.
Part II
Go to http://phet.colorado.edu. Click on PLAY WITH SIMS > CHEMISTRY> GENERAL
CHEMISTRY> RUTHERFORD SCATTERING (**This MUST be done on a computer!)
Step 1: Click the RUN NOW button to load the simulation.
Step 2: Before you TURN ON the GUN, make sure the following are selected:
1-The tab at the top that is selected is the RUTHERFORD MODEL
2-Alpha Particle Properties:
 ENERGY of the alpha particles is half-way between MIN and MAX
 SHOW TRACES box is checked
3-Atomic Properties (we are going to examine something other than gold):
 Number of PROTONS is 20
 Number of NEUTRONS is 20
Step 3: TURN ON the GUN by clicking on it and observe what happens when the alpha
particles are fired at the atom’s nucleus. Answer the following questions below:
1. What atom is being represented? __________________
2. What is happening to the majority of the alpha particles (make sure you observe this for a
while before describing)?
3. What do you think is the charge of an alpha particle from this experiment (remember the
nucleus only has positive charges)?
4. What did Rutherford prove about the atom from this experiment?
Step 4: Now, change the following:
1-Select the tab at the top for PLUM PUDDING
2-Keep the ENERGY the same
3-Keep SHOW TRACES checked
Step 5: Turn on the gun again by clicking on it, observe what happens for a few minutes, and
answer the following questions below:
6. What is happening to the alpha particles in this model?
7. Did you expect this to happen knowing what JJ Thomson’s Plum Pudding model looks like?
Explain.
8. How is this result different from the result shown with Rutherford’s atomic model?
Niels Bohr
Find information about Bohr’s atomic model from the classroom copies of the textbook.
1. Describe Bohr’s atomic model and sketch/label that model below.
2. In what ways is Bohr’s model similar to Rutherford’s model? In what ways is it
different?