Download Development of Atomic Theory: Democritus to Thomson

Unit II: Chemical Foundations
Development of the Atomic Theory: Part 1
Learning Target(s): 1
1. Do ideas or theories in Science stay the same? What causes this?
2. Who was Democritus? According to Democritus is it possible to tear a piece of
paper in half over and over? Why or why not? What did this allow him to
conclude about matter?
3. What does the Greek word “atomos” mean?
4. What is the textbook definition of the atom?
5. In 1808 a British chemist and schoolteacher, John Dalton, brought back
Democritus’s idea of the atom. What 4 ideas did his new theory of the atom
propose?
1.
2.
3.
4.
6. In 1897 a British scientist named Thomson discovered that atoms were not
indivisible but were made up of smaller particles. What particle did Thomson
discover and what electrical charge does it have?
7. Thomson showed that electrons were part of atoms. Where did he think they
were?
8. What was the funny name for this model?
9. Draw a model of the atom proposed
10. In 1909 a former student of Thomson’s, Ernest Rutherford decided to test the
idea that electrons are evenly distributed throughout the atom. Draw a diagram
that shows Rutherford’s Gold Foil Experiment. Label it.
11. What did Rutherford discover about the movement of the particles that he shot
at the gold foil? (What did most of the particles shot at the gold foil do? What
happened to a small amount of the particles shot at the gold foil do?)
12. Due to the results of his experiment Rutherford revised the atomic theory in
1911. What were the 3 main conclusions that Rutherford made about the atom.
1.
2.
3.
13. Draw a picture of the Rutherford model of the atom below.
14. Who is credited with the discovery of the neutron?
15. Why are neutrons so important in the nucleus of an atom?