1. THE HISTORY OF THE ATOM

2. Greek Philosophers (400 B.C.)  Aristotle- believed the everything was made of the 4 elements (air, fire, water, and land). Each substance contained a varying portion of each element.  Democritus-believed everything was made of invisible and indivisible particles called “atomus” = ATOMS

3. Ben Franklin -1748 Determined there were positive and negative charges in nature.

4. Antoine Lavoisier-1790 Law of conservation of matter- matter is neither created nor destroyed in any process (you did an experiment with the test tube and the flask)

5. Joseph Louis Proust - 1799 Law of constant composition - any sample of a given compound always contains the same percent of each element by mass. Law of constant composition - any sample of a given compound always contains the same percent of each element by mass.

6. John Dalton-1803 Created the Atomic Theory of Matter Created the Atomic Theory of Matter Contains 4 postulate : 1.Each element is made of invisible and indivisible particles called atoms. (Democritus) wrong 2.All atoms of an element are identical. wrong 3.Atoms can not be created or destroyed in a reaction. (Laviosier) (Laviosier) 4. A given compound always has the same relative numbers and kinds of atoms. (Proust)

7. Michael Faraday - 1839  Suggested there was a connection between the structure of the atom and electricity.

8. E. Goldstein - 1886 Isolated the proton. Isolated the proton.

9. J.J. Thomson - 1896 Isolated the electron. (cathode tube in the journal) Isolated the electron. (cathode tube in the journal)

10. Henri Becquerel - 1896 Accidentally discovered that uranium gave off invisible rays. Photo plates were developed when put close to the sample of uranium. (journals)

11. Marie and Pierre Curie - 1898 1.Named Becquerel’s invisible rays “radiation”. 2.Isolated the radioactive elements polonium and radium.

12. Ernest Rutherford - 1909 1.Isolated alpha and beta radiation. 2.Found all of the atom’s protons were in the center of the atom and called this the nucleus. (gold foil experiment in journal)

13. Robert Millikan - 1909 Found the mass (grams) and the charge (columbs) of the electron. (Famous oil drop experiment done at he University of Chicago.)

14. Niels Bohr - 1911 Proved electrons were in energy levels around the nucleus. (The current model changes part of Bohr’s idea.)

15. James Chadwick - 1932 Found the nucleus of the atom also contained neutral particles; he called them neutrons.