1. Atomic Theory 1

2. Atomic Theory
Theories in science are proposed to explain the evidence available at the time.
As new evidence is discovered theories are adapted to explain new data.
This is the nature of Science.
In the future this will continue.

3. Plato
Democritus BC
Atoms make up the world

4. Plato
Teacher of Aristotle
Aristotle BC
Four Elements

5. The Four Element Theory wetness harmony conflict
Aristotle
Forces
The Four Element Theory
Properties
wetness
harmony
conflict
Water
Wind
coldness
hotness
Earth
Fire
dryness

6. The Four Element Theory lasted for about 2 thousand years because no one tested the theory with scientific experiments.
It was not a scientific theory- which is tested by experiment.

7. John Dalton
Atomic Theory

8. Dalton’s Atomic Theory- 1808
Evidence
1. The Law of Conservation of Mass
2. The Law of Constant Composition- water is 11 % H and 89 % O
Theory
1. Each atom is an indestructible and unique spherical particle
2. Atoms combine in simple whole number ratios to form compounds

9. Hydrogen
Oxygen
Lithium

10. Dalton Theory- Water
1 g H
1 g H
16 g O
18g O

11. Dalton Theory- Water
16 g O
1 g H
18g O

12. Dalton Theory- Water
16 g O
1 g H
g H
x %
= 11% H
89 % O
18 g H2O

13. Having a molecule (atoms combine in simple whole # ratios) explains the law of constant composition.
Still
11 % H
89 % O
No matter how much water you have its still 11% H

14. 2H O  H2O
If the atoms are not destroyed then the mass does not change

15. J. J. Thomson

16. The Thomson Theory of the Atom
Evidence
1. The electrical nature of matter
beta particles
static electricity
current electricity
Theory
1. The atom is made up of positive material with negative particles throughout- like blueberries in a blueberry muffin.

17. The Thomson Atom 1903 + + - + - + + - + - + - + - + - + + - + + - + -
+ + -
- + -

18. Ernest Rutherford

19. The Rutherford Atom 1911
Simulation
Evidence: Gold Foil Experiment
% of alphas are not deflected
% of alphas are radically deflected
Theory
1. Most of the atom is empty space.
2. There is a small dense nucleus in the center of the atom that makes up most of the mass. Electrons circle the nucleus randomly.

20. Be - The Rutherford Atom 1911
Scale: nucleus is home plate; atom is the baseball field Be
Nucleus- is small but has most of the mass
Nucleus- 4 protons and 5 neutrons -
Electrons

21. Cornelis Escher
Discovery of the Nucleus
Size of the Atom