1. Unit 1: Atomic Structure Honors Physical Science
Evolution of Atomic Theory

2. Democritus – 400 B.C. Greek Philosopher
Imagined particles that were indivisible
Constituents of matter
Atom comes from “atomos”
Opposed Aristotle

3. Aristotle – 350 B.C.
Widely accepted theory that all matter can be continually divided.
Set science back for thousands of years.

4. Alchemy A pseudoscience that superceded scientific discoveries.
Alchemists attempted to turn metals into gold and developing the “elixir” of life (able to cause immortality and create life).

5. Pierre Gassendi - 1650 Reintroduced Particulate theory
No experimental evidence
Supported by Sir Isaac Newton

6. Antoine Lavoisier - 1778 Developed Law of Conservation of Mass
Explained combustion

7. Joseph Proust - 1799 Developed “Proust’s Law” using copper oxide
Later renamed, the Law of Definite Proportions
Nearly discovered the Law of multiple proportions, but his data used percentages instead of weights.

8. John Dalton
First to develop an atomic theory. It has 4 postulates.
Each element is made up of atoms
Atoms of the same element are identical in mass and properties. Atoms of different elements differ in some way.

9. John Dalton
Compounds are made when atoms combine. If elements combine in more than one whole number ratio, the resulting compound has different properties
Chemical reactions involve the reorganization of atoms.

10. Eugene Goldstein
Discovered the proton using a cathode ray tube.

11. J.J. Thomson - 1897 Determined the mass/charge ratio of the electron.
5.69 x 10-9
Used the cathode ray tube
Proposed a model of the atom that was mockingly called the “plum pudding” model

12. Robert Millikan
Determined the charge of the electron using the famous oil-drop experiment
1.60 x 10-19
From this and Thomson’s value, the mass was calculated to be 9.11 x 10-28g

13. Ernest Rutherford - 1911 Performed the famous gold foil experiment
Determined 3 things
The atom is mostly empty space
The nucleus is positively charged
The nucleus is a small dense part of the atom

14. Gold Foil Experiment

15. Gold Foil Experiment

16. Niels Bohr - 1913 Observed spectral lines for hydrogen
Proposed an orbit theory of the electron around the atom.

17. Bohr Model

18. Hydrogen Spectrum

19. Louis De broglie
Suggested that matter could exhibit wave properties
Observed diffraction patterns in electrons

20. Erwin Schrödinger - 1926 Developed a wave equation.
Mathematical function that described the nature of the electron

21. James Chadwick
Discovered the neutron