1. 1803
Key words
John Dalton
Father of the Modern Atomic Theory

2. Postulate #1 True or Wrong?
Experiment/postulates
Know all 5!!!
Elements are composed of atoms, which are very small, indivisible, indestructible particles.
True or Wrong?

3. ……we know about subatomic particles.
Wrong
……we know about subatomic particles.

4. Postulate #2 True or Wrong??
All atoms are of the same element are identical.
True or Wrong??

5. Wrong
….they aren’t exactly the same because of isotopes (atoms with same number of protons but different number of neutrons).

6. Postulate #3 Atoms of different elements have different properties.
True or Wrong??

7. Postulate #4 True or Wrong??
Atoms combine in small, whole-number ratios to form compounds.
True or Wrong??
Two Hydrogen
One Oxygen
H2O

8. Postulate #5 True or Wrong??
Atoms of one element cannot change into an atom of a different element during a chemical reaction.
True or Wrong??

9. Experiment
1897
Key words
JJ Thompson
Electrons discovered by experiments with cathode ray tubes
+ magnetic field
- Magnetic field
Electron stream w/o applied magnetic field
Electron stream after applied magnetic field
**He was finally able to show that the beam could be deflected by an electric field, and thus consisted of NEGATIVELY CHARGED PARTICLES (AKA ELECTRONS)
discovery
sketch

11. 1904 JJ Thompson again… Another Experiment
Published atomic theory that’s now known as Plum Pudding Model
Thought electrons moved randomly in a positively charged, amorphous “pudding” or cloud
Another Experiment
Actual plum pudding!

12. 1909
Key words
Rutherford
Gold Foil Experiment
nucleus

13. 1911 Experiment Discovery sketch Rutherfords discovery:
1.The atom has a dense, positively charged core (aka nucleus) which contains most of the mass.
2.Most of the atom is empty space. The electrons are somehow moving around the empty space.
Discovery
sketch

16. 1915
Important words
Discovery
Negative electron
Niels Bohr proposes the Bohr Model, also called the Planetary model
This states the electrons orbit the nucleus much like planets around the sun (which we now know is not exactly how electrons travel!)
Nucleus (positively charged)
sketch

18. What we know now! Watch this video…
Now we know that electrons travel around the nucleus, not in circles but in different shaped patterns!