1. How we got to where we are now
Atomic Theorists
How we got to where we are now

2. Law of Conservation of Mass
Who: Antoine Lavoisier
Matter can't be created or destroyed
When: 1785
Where: France

3. Law of Definite Proportions
Who: Joseph Proust
Compounds – Elements put together in
fixed ratios of small whole numbers
C + O2  CO2
When: 1797
Where: France

4. Law of Multiple Proportions
Who: John Dalton
Two elements can form more than one compound
The subscripts of the elements in the compounds will be small whole numbers.
C + O2  CO2
C + O2  CO
Where: England When: 1803

5. Who: Aristotle What: All matter is a combination of fire,
air, earth or water
When: 350 B.C.
Where: Greece

6. Who: Democritus When: 400 B.C. Where: Greece
What: Matter was made of indivisible
substances he called atomos
(1st talk of the atom)

7. Who: John Dalton What: Solid Sphere Model (1st atomic theory)
Elements are made up of indivisible particles called atoms
Each element was composed of the same kind of atoms.
Different elements were composed of different kinds of atoms.
Compounds are composed of atoms in specific ratios.
Atoms are not created or destroyed in a reaction.
When: Where: England

8. Problems with Dalton’s Theory Today
(issues that weren’t known about ..yet)
Matter is composed of indivisible particles
There are electrons, protons and neutrons
All atoms of a particular element are identical
There are isotopes
3. Different elements have different atoms
Atoms combine in whole number ratios
Atoms can’t be created or destroyed
Nuclear explosions destroy matter

9. Who: J.J. Thomson What: Atoms aren't smallest particle
Conducted experiment with a
Cathode Ray Tube
Particles had a negative charge
(discovered electrons)
Model = plum pudding
When: 1897 Where: England

10. Cathode Ray Tube

11. Who: Robert Millikan What: Experiments to determine mass of electron
Conducted the oil drop experiment
Verified that electron is negatively charged;
1.6 x coulombs
No new model
Where: America When: 1910

12. Millikan
Oil Drop Experiment

13. Who: Ernest Rutherford
What:
Conducted Gold Foil experiment
Proved nucleus is dense, positively charged core of atom
When: 1911
Where: America
Model = Stationary Planetary

14. Rutherford’s Experiment
Gold Foil Experiment

15. Results of foil experiment if Plum Pudding model had been correct.

16. What Actually Happened

17. Who: Niels Bohr What: Pulsating Planetary Model
Electrons can move between energy levels
When: 1913
Where: Denmark

18. There were many people involved with developing the mathematical
process to determine the path of the electron. One of these men was Schroedinger.
What: pulsating orbital model
When: 1926
Where: Switzerland

20. Who: James Chadwick What: Confirmed existence of neutron
No new atomic model
When: 1932
Where: England